- Draw the game - in a graphics programme or on paper, but draw it to scale. That way you can see the layout you have in mind and see if everything will fit.
- You need only the main ideas to start with, and the drawing.
- What's going to be unique about the game?
- What's going to be the fun aspects?
- How do you win?
- How do you lose?
- Will there be achievements or rewards?
- What happens when you die / lose?
- Decide on your target devices (i.e. pc or mobile etc.) and keep that in mind when you plan out the size and extra effects.
- Create a small prototype of the game just using basic shapes - sometimes a game sounds fun in theory, but isn't when it's actually written. It will also give you ideas of what works, what isn't going to work, what is going to be a problem to program or to create graphics for etc. When I have the game working on a template level and I can see that it's viable - that's when I start planning the detail and the things to make it look pretty. I've also learnt that when a game is extremely boring to develop that it is also going to be extremely boring to play - I abandon those or rethink the ideas.
- Make a list of all the global variables and data structures that you will need (for example, score, health, weapons. But don't go into too much detail - just the basics - it's enough to know you need to plan out the weapons in a data structure without necessarily listing every weapon you can think of. You can add those in as you're working on the game and most software is flexible enough that a list can grow or shrink without much effort.
- Note down all the interface / menu items you need and decide where and how that is going to be implemented - will the buttons always be on screen or will you have a pop-up menu? It's important to create with the pause / music / sound options in mind from the start, because they should be settings where the user can choose and you need to plan for that when you code - i.e. you can't just say, play sound, you have to say - if user wants sound - play sound.
- I probably have at least 20 games written down and planned in detail that I've never written. When I'm really excited about a game idea, I tend to plan them a lot less and jump into creating them sooner. But that might just be me...