First thing you should do, is learn everything you can about mining and how it all works. Next thing you should do is calculate and see if it will be profitable for you to mine with GPU, and which GPU you would need for making profit. Electricity is important factor in mining, because if your bills are higher than your income... well that's bad thing.
When you have done that, next thing would be finding good coin to mine. Some basic information about profitability of coins you can find on
WhatToMine and
CoinWarz.
After that you will need certain mining software, but that depends on which coin you want to mine. Also know that solo mining doesn't pay off, unless you have some serious mining rig. So you would need to find some mining pool.
This are some basic things that comes to my mind at this moment, if you have more questions just ask.