I personally use a spreadsheet but I'm sure there are better way to do it.
Do you know any good websites/apps to do it?
I
HIGHLY recommend
https://altpocket.ioIt is such a great website, with good looking layout and all the information you want from your coin(s)
Thanks for the share its really a nice handy website and clean user interface too, I was actually expecting this to be a fee paying site but to my surprise its FREE! Otherwise before I knew of this website I avoided keeping track of my trades because on bad days i made some losses which i do not like to account for...