Before you start thinking that this is too much of a task, I'm talking about using a tutorial or references. All the software listed above have plenty of tutorials on their websites or youtube for making a basic game (video tutorials are usually the easiest to follow). Do the simplest one you can find, follow it step by step and then come back here.
Step 4: Tweak your game
This is where things will get interesting. Here you will take your tutorial game and start tweaking numbers, changing sprites and modifying other attributes.
This is all about playing with the game to see if you can do something interesting with it. This is a great way of learning some game design also as it teaches you what works and what doesn't.
For example; say you make Pong. What can we tweak here? Well lets see. How about the ball velocity? or the paddle velocity? We could allow the paddle to be moved closer to the center or even shrink or enlarge the paddles. Even better, how about we add multiple paddles we can control separately? and instead of the paddles moving up and down, maybe they curve or move in a circle. You can see the possibilities here I'm sure.
Step 5: Repeat Step 3 and 4
Repeat these steps until either a Game Jam starts up or until your confident to start creating something yourself.
Important: Ensure you get very familiar with your chosen piece of software. If you have started doing small games yourself, get used to how the art and music need to be done as well using previous examples.
Step 6: The Game Jam
The home stretch. You should now have all you need to make something for a game jam. They happen all the time online and there may even be something locally you could join so investigate this. I will have some links at the end to sites that track game jams.
Preparing for the jam - Solo
From your tutorials you should have a good idea what type of assets you need to make a game. Images, text, sound, etc... You will need to know where to get these without breaking copyright (that is if your not making them yourself). Use sites like freesound.org and opengameart.org to find Creative Commons copyrighted assets, and don't forget to credit the creators of the assets you download in your finished game!
Preparing for the jam - Team
The main difference with teams in game jams is that assets are generally going to be made by individual team members (mostly). I think it is vital that all team members have their own tasks or individual contributions. This means, if the team happens to be 4 programmers, ensure only 1 is programming the game while the others do art/music/writing etc... Things just get too messy otherwise. Decide this beforehand if possible or at least have a good idea what everyone is capable of.
How to participate
There is a basic structure to the Game Development process everyone should know when doing a Game Jam. It is essentially a cut and paste version of the Game Development process in large scale games.
Deployment and Publishing
* = Playtesting should be done throughout but more heavily as the game nears completion
So the theme is announced and its time start. Brainstorming will be the shortest thing you do but should be done for at least 30 minutes. Come up with several ideas/concepts and write down how they will work. Don't linger on one idea for too long!
Next start prototyping your ideas. Now this does not necessarily mean "build the game", it just means test out the idea in some practical way, quickly. The more minimalistic the better. This can be drawings, paper cut outs, bullet points or primitive game building in your software. With this, you can eliminate the ideas that don't work or are too big for the jam.
Important: Possibly the most important decision you and/or your team make in the jam is the scope of the project. What I mean here is how complex or minimal it will be based on your current skills and the time frame you have allotted. This can be very tricky to get right, especially at first and is probably the number 1 reason why so many Game Jam virgins fail the first few times.
Once you've picked an idea that works and is within the scope of the jam, its time to start building! Always start out by getting something playable on screen asap, if you haven't already done that that is. If solo, it would probably be best to get the core mechanic of the game working perfectly first before worrying about other mechanics or assets. Playtest constantly or if you have a team member not making assets, make them do it, it's even better with feedback from someone else.
Keep an eye on the clock while doing this as you want to make sure you have enough time towards the end of the jam for the polish section.
Once everything is working and all the assets are in, time to polish. This can mean adding UI elements (scores/healthbars) or sound effects or additional animations or title and credit screens. It's all about making it look presentable and understandable. Sometimes it might even be a good idea to get someone not on your team to playtest it and find out if it makes sense to them.
Finally there is deployment and publishing. Whatever platform you making this on, make sure that once you deploy that exe or flash file or whatever it is, ensure its working on another computer. No point in distributing it when it only works on your pc! The publishing arrangements will usually be provided by the Game Jam organizers and have instructions on what to do. But remember there are always sites like kongregate and itch.io which can host your game.