Beginner-analysis 3
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when Qh5 better is Nc6 to defend the e5 pawn. If that does occur then opponent bishop emerges at Bb5 threatening scholar mate at f7 (parham attack).
Better than 5. ...d5 is 5....Kh8 refuting 6. Bh3 cause of the pinned pawn.
8. ...g6 better is 8. ...gxh3 at least equalising material wise.
10. ...Na6 not a good move de-centralises the knight. Note the pressure being put on ur d5 pawn. Your task must also be to remove that bishope on h3 which could produce mate threats if u queen and bishop are deflected.
At move 17 as pointed out ur pawn is isolated because of the defenders it lacks.
I would concluded my anaylsis here. What u need is some insight into strategy and tactics. For tactics i recommend chesstempo.com (google it). For strategy i suggest read chess books (invaluable). U should improve urself positionally and tactically that way. Hope it helps u be a better chess player.
Cogwheel was much better when they were rated 979.
Thanks Scottrf and MetalFactor for your helpful analysis! It's a great help!
I think Cogwheel thinks that my opponents play was stupid. I can only state how it felt, when I played him, and I felt under pressure, which probably also had to do with blunders, which created unnecesary pressure. Maybe in time I'll also feel his play was stupid, lol.
Quote: until 1800 your first name is tacitcs, second name is tactics and third name is tactics.
To defend well, look at what your opponent is trying to do. Imagine you're playing at his place. Why did he move 7.Qf3 ? Which move would he hope to see after he's just played 7.Qf3 ?
Material is important : ask yourself "is he threatening any of my pieces with his last move ?" Do it on every move.
In your comments, you can't just dismiss your blunders. It's important you try to understand why they happened : not paying attention ? not asking yourself what your opponent was trying to do ? not able to concentrate during the game because of external factors ? not noticing a new line had been opened, etc.
Know your enemy. Know yourself 
Hello guys!
I felt totally lost in this game. I didn't really know what to do - most of the time - against this aggressive and strong play.
I haven't annotated any moves, because most of the time I felt that I was on my heels just trying to minimize the loss.
Besides the obvious blunders, are there some main things I could have done differently?
And is there e.g. an idea I should stick to against an aggressive player? Is it just going to be defense-defense-defense against something like this, and then wait for an opening?
Thanks in advance!