You received a guideline with your déclaration d' impôts that should explain most things but I'm not sure they will have it in English, try calling the tax authorities (the link is further along this post). I see they have a
software to help you complete your taxes, I would use that, it's much easier and some softwares available tell you where you can make deductions.
Depending on you salary, I would strongly recommend getting a specialist to do it for you as the savings you can make are often more than the cost of someone doing the work for you.
Also, make sure you are within the deadline, otherwise they will simply estimate what you earn and you only have ten days to contest what they decide. Usually, they estimate very high as a sort of punishment, so it's not worth it! If you can't make the deadline, contact them ASAP instead of hoping it'll disappear, they tend to be surprisingly understanding and happy to help.
I don't know how good your French is as
the Geneva tax authorities seem to only have their site in French. There are quite a few explanations there too.
If you do decide to do the thing on your own, make sure you gather every single bill you can find and divide it into medical costs, costs incurred from work and money given to charities and political parties (all I can think of off the top of my head). Get your bank statements and any other things that show your assets or, if applicable, any debt you may have.
Doing the proper deductions essentially decides on how little or how much tax you will have to pay, which is why I recommended a professional if you earn more than just average pay. I do my own tax but I only have a part-time student job so making a mistake is not a question of thousands of francs, more like a hundred. And I work in the tax department of a large company so if I do have a question, I ask one of my bosses.
Once you have all your forms filled out, photocopy them as well as the bills you will need to enclose. The original form and the copies of the bank statements etc. go to the tax authorities, the other stuff you keep for your files. Depending on your situation you can just more or less copy what you filed this year the next year too. I do it like that and I've been able to reduce the time I need to do my taxes to roughly 2 hours, especially as I file all deductible things in a special folder right away.
Hmm, don't know if it's any help but if you don't understand some of the phrases in French, just ask, I'll probably be able to translate them for you.