Play with people of similar skill level. I think that's the big one... Very good bridge players tend to take bridge much more seriously, which is probably how they got to be very good, eh? But that means they tend to be far less tolerant of people playing slowly, thinking things through, or making rookie mistakes.
That is a broad generalization of course, everybody is different... In the end though, this is the internet. Annoying jerks thrive here, where there's no real repercussions. The only way they can win is if they stop you from having fun. Cultivate a thick skin.
Regarding beginner play, I wrote a little thing to analyze the results from the bridge base myhands list for myself, and I ran your name through it.
Avg IMPs: -0.45
Offense: -1.00
Declarer: -1.99
Dummy : -0.34
Defense: +0.02
So just at a glance, -0.45/board is a bit below average but not horrific -- Just fine for a beginner. It appears when you play as the declarer, you perform worse than when you're on defense or when your partner is the declarer. Nothing wrong with that of course, but maybe that might be the area where you could see the biggest immediate gains, eh?
The most important I've learned is to stop before you even play that first card off the dummy on that first trick. Examine every suit, note how many combined cards are in the suit, what honors are missing, did one of your opponents bid that suit, etc. Then construct a plan for the entire hand, start to finish. For a novice it's probably going to be something vague and fuzzy like "Lead out trump, then set up that 9 card outside suit" or "Set up a cross trump because I need to get rid of these losers before leading out trump". But even a fuzzy or sub-optimal plan is infinitely better than having no plan! :-) Over time, your plans will become more cogent as you start to take into account transportation, who to finesse for what, etc.
The "Learn to play bridge" software from ACBL has a section entitled "Planning the Play". I recommend going through it several times since there's too much to take in at once. Even though I've been playing years, I sat down and went through them. It still caught me a few times making the wrong plays, then it explains WHY they were the wrong plays. Very valuable :-)
The other one beginners often fail to grasp -- Position is
hugely important. The later you play on a trick, the better. Sometimes the best thing you can do is intentionally losing a trick (often to a specific opponent), so you get to play 2nd and 4th instead of 1st and 3rd.
Anyway, just some rambling thoughts. Don't let the jerks get ya down. :-)