First I'll provide some context by introducing myself. I'm a 4th year student/graduate from the HKU in the Netherlands. During my time there I've created several games with the aim to release them. Not all were published, for several reasons.
The last two years I spent working within my own company (Speelbaars) and we were supported by school on our debut title 'Lumini'. I'm not that good at making constructive stories, so I'll provide you with a handy bullet-list about stuff I've learned over the past few years.
1) Don't think about making a game, start MAKING a game.
2) Don't talk about ideas, show ideas (prototype!).
3) Don't try to do everything by yourself.
4) Learn something about every part of development (programming, design, art, business).
5) Trust the people you work with,
6) But still get your contracts done in time.
7) Plan ahead, especially for longer projects.
8) Don't be afraid to ask for help, information or feedback.
9) Don't be afraid to kill your darlings, omitting is the art of creating.
10) Learn what a 'minimal viable product' is and means.
11) Make mistakes and learn from them.
12) You can't prevent every mistake, you will make them, accept that.
13) Don't panic; there is always a solution.
14) Make a game for your audience, not for yourself.
15) You won't reach your potential by staying in your comfort-zone.
16) You're competing with thousands of developers for the same spotlight.
17) Don't let this scare you.
18) Not everyone will like your game, that doesn't mean it's bad.
19) There will always be people that will like your game, you just need to find them.
20) Almost everyone you meet in person will tell you they like your game, even if they don't.
21) You (probably) won't get rich by making games.
22) You (probably) won't get famous by making games.
23) Your games will have an impact on someones life.
24) Don't let others discourage you.
25) Be realistic about your future.
26) You will have to talk to others a lot!
27) You'll have to do the social media thing.
28) No matter how much you hate Twitter or Facebook ;-)
29) Networking is important.
30) Don't dismiss anyone you talk to as unimportant, everyone has value.
31) Never be rude to anyone.
32) NEVER EVER(!) burn bridges.
33) Money isn't evil, you'll need it.
34) You don't have to sacrifice creativity or vision for money.
35) You will struggle with the balance between vision and money.
36) You're never done learning, about anything.
37) There will always be people that are better at something.
38) You'll get jealous, but will have to deal with it.
39) Never bare a grudge, it's not worth your energy.
40) Responding to trolls isn't worth your time.
41) People will try to use you for their own gain.
42) Those people can still be your friends, they just think you offer value as well.
43) Your family can help you, even if they don't understand games.
44) Make contact with your local gamedev scene, you'll make friends and learn stuff.
45) Always try to help others when they ask, no matter how successful you've become.
46) Remember that everyone started at the bottom.
47) AAA isn't soulless, people making them are just as passionate as you are.
48) Publishers aren't evil, most of them are awesome.
49) Even the biggest publishers do their best, but big companies have a bad communication structure in general.
50) Go to events if you can, even if they're just local and small.
51) You do want to sell your game on Steam if it's for PC (it's 99% of your potential market).
52) But also sell it at smaller platforms (Itch.io, GoG, etc).
53) I don't know much about console markets, sorry :') (But you do remember tip nr.right?).
54) If someone tells you, you can always contact them for help, they probably mean it.
55) If people don't respond to your e-mail they probably haven't read it, because their inbox is flooded.
56) Don't be afraid to send a follow-up e-mail, but don't be 'that guy'.
57) If you've got some kind of relationship (IRL, Online, etc) with the person you try to contact, social media is a better option then e-mail in general.
58) Always start with the least amount of necessary people on a project.
59) Down scaling a team is something you want to avoid, up scaling is always an option if needed.
60) Look at everything around you for inspiration, don't be stuck at just looking at other games.
61) Inspiration can come at anytime and anywhere, always have a way of writing it down.
62) Game design documentation is necessary, no one likes it though.
63) You'll need someone in your team with a business focus. That person can still be a dev.
64) Marketing will need your full attention.
65) You'll need to market your game as early as possible
66) Remember that everything that goes online, stays online though.
67) You're always responsible for what you say (online). Even when sad, drunk, sick or whatever.
68) Some people will try to attack you on your weaknesses.
69) Again, those people aren't worth your attention.
70) Do try to learn something from what they say, there is always some truth behind everything.
71) You can also call a person if you really need their attention.
72) Grammar check any text that you publish.
73) Strategies that worked yesterday, won't necessarily work tomorrow.
74) Always be original, don't copy other people's work.
75) Always read stuff that you need to sign with a signature, ask if you don't understand something.
76) When approaching journalists, think about what story you want to tell.
77) 'I just want to make fun games' isn't a great story
78) Avoid the use of buzzwords like innovative, immersive, unique, etc as a way to describe your game.
79) Think outside the box when monetizing your game.
80) Multiplayer games are fun to make, but really hard to sell when you're just starting.
81) Winning awards is nice, but generally awarded by people that will not buy your game.
82) Although awards won't sell your game, they do give you exposure with media.
83) Media attention is great, but what really makes you game successful is people telling their friends about it.
84) Don't shy away from giving away free copies of your game, even to smaller sites/ youtubers/ streamers.
85) If one free key convinces two people to buy the game, you make more money than it cost you.
86) Don't buy games from friends, because they're your friends, buy the game because you want to play it.
87) The reason for this is that if you do, other 'friends' will expect the same treatment.
88) Nowadays, if your game is stuck on Greenlight for more then a month, it's just not good enough.
89) This doesn't mean it isn't good, you just need to go back to the drawing board.
90) If your game isn't remotely fun after the first few weeks of development, it probably won't be anytime soon.
91) Ditch that concept and start something new, instead of trying to fix it. Chances are it'll never be worth the time investment.
92) Every person you hire will cost you money. Even when it's a revenue share.
93) Don't forget to spend time on hobbies outside of gaming.
94) Don't spend all your time on a project, you'll lose motivation faster. Take breaks.
95) Don't be afraid to invest money, it'll be worth it in the end.
96) Avoid going into debt at all costs.
97) If someone promised you something, don't be afraid to remind them of that promise.
98) Don't be afraid to cash in favors.
99) A good game has meaning and value for a player.
100) The easiest way to accomplish this is to make your game 'fun'.
101) If you lose motivation, and you will at some point, take a step back and remind yourself why you're doing this.
102) Fights will happen in a team and that's OK. Just be sure it's about something important in the game.
103) Also be sure to really listen to concerns that people have in your team, even if you don't share them.
104) In general, never forget it's a team effort.
105) Never hold back critique when someone asks you for feedback, but let it be constructive.
106) When pointing out a problem, be sure to consider possible solutions.
107) You're responsible for your own successes and failures alike.
108) You're never unique in your problems, someone already dealt with them somewhere.
109) Get comfortable with presenting in front of a crowd and public speaking.
110) 'No' doesn't necessarily mean 'Never'.
111) Submit your game to competitions and selection procedures for events.
112) Remember that games are made to be played by people. Don't be afraid to let someone fail at your game.
113) Some of your players will be idiots, design your game remembering this fact.
114) But never expect your players to be stupid, always take them seriously.
115) Never be discouraged when trying to get your game noticed, keep pounding on that door till it opens.
116) Playtest your game and iterate a lot on it.
117) Collect data while playtesting, but don't forget to follow your gut feeling as well.
118) If an offer sounds to good to be true, it probably is.
119) When you're speaking from experience you're never wrong.
120) But your experiences don't have to be the same as someone else's.
121) Never lie just to fit in or be part of a conversation.
122) Don't be afraid to admit that you don't know something.
123) Have one person be responsible for the PR and trust them to make the right decision.
124) You'll have to release your game at some point, even if that means you're not 100% satisfied.
125) Never give up!
Some of these might not be clear enough, if you want me to elaborate on some of these points don't hesitate to contact me on Twitter (https://twitter.com/ithunn) or send me an e-mail (steven[at]speelbaars[dot]com). Really, don't be afraid to ask ;-).
If you don't agree with me, please let me know why, so we can learn from your point of view as well.