So I'm making this OOTP Tips and Tricks thread, where I'll post a few "did you know you could do this" things and I hope that you do too, because I'm far from an expert myself.
IMPORT VIA FTP
So, we all know how to "Export via FTP" but did you know that you can "Import via FTP" as well?
This can be useful for when the game crashes and you don't want to re-do all your work, or mis-clicks where you want to restore to a previous point without re-downloading the file.
So go to your Rosters & Transactions page, and click on the "ACTIONS" drop down on the top right. From there you can Import via FTP and it will load the last file that exists on the server from your previous upload. Of course, this is only useful if you've already exported for the current game date.
BONUS!
While we're in that menu, you can also Import/Export to File. This drops your team file into:
C:\blahblah\OOTP Baseball 21\saved_games\Brewster.lg\import_export
Or if you're on mac it goes to the mac place.

The file is called team_##.ootp
But what would I use this for, you ask? You could send it to yourself to load on another computer, or you could send it to Matt if you're unable to export via FTP.
RE-DOWNLOAD CURRENT LEAGUE FILE
Handy if you made a mistake/want to undo something and need a fresh file without doing a full re-install.
Navigate to OOTP\saved_games\brewster.lg\settings and delete "online_league_file_time.cfg"
Return to game, and download as usual.
FILTER BY SHORTLIST
I just came upon this realization today, and I'm sure I'm not the first one, but I'm willing to bet that at least one person doesn't know they can do this. I always struggle with viewing the draft class in game for multiple reasons, and I usually make a spreadsheet for analysis out of game. But I like to do a final comparison of my choices in-game before I actually pick.
Anyway, today I realized that I can add already drafted players to a shortlist, say, "DRAFTED" and then set a custom filter on the draft class to not show guys that I add to this shortlist. Makes it so much easier to look at who is left to be drafted.
Obviously this is not sustainable for later round drafting, but for the first couple rounds, maybe you find it as useful as I do.