So it's been about another two weeks and I've made a few more observations from playing MtGO. Some are specific to online play and others are just good common sense practices.
Watch Your Stops
If you're not familiar with the Magic: the Gathering Online client, it has a feature called "stops" which are exactly what they sound like--a point in the turn where the client stops to ask for your input. The stop location options are all at priority passes as you leave phases and steps, of course, so you have a chance to act.
Some people will set every stop on so they get every chance to act and others will be selective. Personally, I have a few that are on all the time (opponent's end step, opponent's enter combat, my enter combat, etc.) Then, if I need to act during my opponent's upkeep or draw step I enable it on the fly before we get to that point.
Basically, what I've learned is that if you're not thinking ahead you'll miss the right time to act. Also, if you're a real scrub, you probably have all the stops on (like my upkeep) and you're draining your own clock when you walk away after your turn thinking it won't stop until my main phase!
This is probably the most often repeated phrase and one of the most written about pieces of advice--don't go on tilt when you are losing, when you are drawing poorly, when your opponent "just has it," or when the numbers just didn't add up (locked out of top 8 by 0.02% on breakers.)
It does you no good to tilt. Just find your out (see observation #3 further down) and play to it. Granted, you have no real "out" if you've just been locked out of top 8. In that case your out is running for coffee or playing side events.
Learn Your Outs
There is a "way out" of almost any situation. The way you learn them is by playing and by thinking about playing through as many situations as possible. Honestly, this is my main goal with playing extensively on MtGO.
I've played against a number of opponents lately who just scooped up when they still had a very viable out worth playing to (drawing Path to Exile, finding the combo piece before I can draw Lightning Bolt, etc.)
On the other hand, I've had some opponents who--rightly--have forced me to walk through my win so that they get all the draw steps they are entitled to in order to find their out. In fact, I've been doing that lately. Even if I know the only out is a weak one, I want to see how hard I have to work and what things I should do to optimize my odds of drawing it.
That's how you win at Magic, after all: you play to your outs. If you get to them, great. If you don't, don't tilt (see above.)