First things to do when joining a table

Also:
I started paying closer attention to bet sizings and write down what size they used when I see a showdown.

This helped me alot to make better calls/folds lately ( atleast i think so )

I used to think that online short stacked were weak players who were trying to move up and target them appropriately. However, I have learned that this could also mean a tight (good player), player playing multiple tables who is making easy, context free decisions.

The best advice I can give upon joining a new table it to pay attention to players action. Basic obviously, but often overlooked.

If you have zero info on the players (no previous hands/notes), i wouldnt really put much trust into those 15-25 hands sample sizes. I remember personally having like 80% vpip after about 30-50 hands at the table - i just didnt get dealt a card below a jack in those hands. What i would do is pay attention specifically to the non-showdown action (you are already probably watching the showdowns) and make note of anything that you personally would almost never do. UTG raises and HJ/CO calls? Might not be a good player. Off the top of my head (the weird **** i have seen just today at 2nl): stuff like limping, weird sizing (7bb open UTG or min 3b in SB), open shoving/3b shoving 200bb into 4bb pot, excessive donking, raising for all but 1bb and folding when reraised (200+bb pot, 1bb to call) etc. The hand might not go to showdown, but you will know from just that one action that theres a good chance this is not a good player.