Keep an eye on your gear. Not only the level of it (ilevel) but condition as well. If you fail too often, they will be broken and less effective. Get used to repair them often.
At some points in the game, we will reach "Zenos's fights"-kinda of content that relay more on damage input or on mechanics ( I remember lv 70 or 60 Scholar quest job that made me nuts on all those failures to save the NPC).
In those cases, watch out the mechanics. Some NPC dialogues give us a hint about what to do.
And, if you get stuck on them, just watch a video tutorial. There is no shame at it! I do that a lot of times! In fact, some savage contents you can watch tutorials before attempting the run. This could make yourself less helpless to the party. And if you want a suggestion, watch the mtqcapture channel. She goes direct to the point in all stuff.
And, don't worry too much on your failures. All of us die eventually

(one more often than others, but...).
About pressing buttons, just calm down. In time, you will get used to the combos and avoidance of AoEs. As you repeat content, some bosses will become far easier and predictable (an example: Titan). So, go on your pace. There is no need to rush all knowledge on all mechanics and all bosses. The game is designed to be very kind to everyone, since you make yourself open to learn your on job and the basics of combat. But again, you can do all that slowly.
Oh, and try to find kind people to play with inside game. I had a lot of help in my playing time which was why I became myself a kinder person today. Kindness is always a good stuff to play anything
