Collector/Seller tips: Organization
Organization may seem like an obvious thing, but I can tell you that both as a collector and seller, it's something I know I personally struggle with.
One thing that has worked for me is buying longboxes so that I can divide players into sections. Now, I don't put EVERY card I find of players into these, but I do put autographs/Jersey cards/#d stuff in there.
I do so for PC stuff that I know I'll be keeping permanently, or at least for a good chunk of years, and then I also keep a separate one for players that I think are on the up and up, or that I deem "prospects."
One side thing that I do for football cards, is that I keep autographs (rookie tickets) from Panini Contenders in their own section together. Then when the season starts, I keep tabs on each player, waiting for the perfect time to sell their rookie ticket auto. I do this, just because when someone gets hot, those rookie tickets seem to hold good value.
This helped me specifically at one point when Trevor Siemian first got his shot last year. I was able to very quickly find his Rookie Ticket auto, and move it quickly at its highest selling point.
Take these ideas with a grain of salt, but you may just find that they work for you as well.
The real point of this is finding your own rhyme and reason so that you are spared the headache of finding cards when you need them later.