Without sounding funny, it all depends on what your goal is really. You could have a seperate sheet for different games within the same spreadsheet and if you are looking at tracking your bankroll totals, then have a summary sheet too that all the data you input can feed into to show average positions, average winnings etc etc.
There are plenty of existing free sheets you can get from places like
www.twoplustwo.com - you could look at a few and get ideas on what info other people store and then maybe extract the best ideas from a few different ones and put them into your own.
I don't really track my games except stt's. I have a spreadsheet from twoplustwo that you input the position you finish in and it works out jazzy stuff that I don't really look at but it is useful to see how I'm doing in my quest to reach the fpp requirement for the Stars tourney and also shows me when I should be thinking of moving up a level.