"What are your preferred knots at each end when tying a guyline from tie-out to tree?"
I learned my knots, remembered them for one trip, and then forgot them. Next time around I bought a set of six of these tensioners. They come with a little slip of paper showing how to use them, which I kept with them so I wouldn't have to remember anything. Worked great. The added weight is 0.12 oz for six tensioners, which I consider negligible.
"How do you get the sticks to stand up when pitching an A-frame (maybe mine were too heavy?)"
I don't carry trekking poles, and I gather you don't either, but I've never used natural, found sticks for this. If I'm below tree line, I usually pitch my tarp by tying it to one or more trees. If I'm above tree line, then I may not be able to find sticks; for this purpose, I bring along a 1-oz carbon fiber pole. (Bought it from fibraplex, who are infamously slow about filling orders.)
"Do you always use guylines or does anyone sometimes stake the tie-out directly to the ground?"
Sometimes I do that if I'm pitching the tarp just on the off chance that it will rain, but I don't really expect it to rain. It takes a little less time, but if you do end up having to sleep under the tarp, it puts the tarp closer to your face, which will be less comfortable. In the Sierra, where conventional wisdom is that it never rains at night, I put in a varying amount of effort depending on my perceived risk of rain. From lowest to highest level of effort, this is: leave the tarp in my pack; put the tarp (in its stuff sack) next to my sleeping bag; stake the tarp directly to the ground on one side, next to my sleeping bag, but leave it rolled up; erect the tarp in a sloppy way, and don't actually sleep under it, but be prepared to get under it in case it does rain; do a good job of pitching it.
"What do you do when the wind is changing directions?"
Curse my fate.
"Titanium stakes don't always stay in the ground when you're staking out the opposite side tightly."
Sometimes if the dirt is shallow in certain areas, you can tie to something else besides a stake: tree, log, rock, ...
Personally, what I need to study up on is better ways of keeping the middle of the tarp from drooping a lot.