First of, write down your idea.
If you plan on various recipes, write them down, look at them, set them into the context of MC or other mods.
Do not start programming unless you have you full idea written down on paper. Even then start thinking about how you will solve the problems that come with you mod, technically or in game (balance).
90% of a mod developers (game designers) job happens on the drawingboard. 65-80% of a programmers work happens on the drawingboard, too. And you need to be gamedesigner and programmer in one person.
Always ask yourself, what is the mod / recipe good for. Do people really need this, do they have some workaround? What happens to other recipes / items / gamesrules, if you really write this mod.