Looking for Advice

Hi everyone,

This is going to be a bit of a long post because I've got a few questions to ask.

I used to play chess at a decent level as a child (usually getting in the top 20% at regional tournaments), and I picked the game up again eight weeks ago, having not played it for 3-4 years before then. I've been playing games on this site most days (no over the board chess), and have steadily improved from ~750 rating to hovering around 1000. 

I'm enjoying playing chess again, but I'm a bit sick of the fact that almost every game I play on this site ends because either me or my opponent has blundered a piece away, overlooked a good move or hasn't seen an attack or checkmate coming. Often by the late opening/early middlegame my opponent will have a better position than me, which they will then use to harass my king with little I can do about it. I often struggle in the endgame too. I hardly practised endgames at all as a child because most of my games would end before then, so I don't have much experience with them. 

In addition, I often find myself in a situation where I'm happy with the position I'm in and I'm not sure what move to make next. When this happens I tend to guess what the best move could be out of a few options, which often ends badly. 

(TL;DR) So the questions I have are: any general principles or advice to follow in the opening/endgame to ensure I don't end up in a losing position after 10 moves, or that I lose an endgame I could have won? Any openings in particular that I should study/practise? 

Also, any advice on how to forsee/avoid/mitigate attacks and checkmates from opponents before I'm in danger? What should I do when I don't know what to do? How would I go about winning games at, say, 1200 rating or higher?

Any other general advice would be greatly appreciated.

Thank you!