Where to start?

what time controls do you play?

i play a mix, mainly on another site - bullet, blitz, rapid, classical rarely) and correspondence

ok. Well there are long games in there. What helped me is puzzles. I used these to help develop my calculation skills. So rather than quick pattern recognition puzzles are do harder ones where it's necessary to explore candidate moves and calculate different variations until you hit the solution. After 8 months and 5 a day my calculation and visualisation skills are much stronger, consequently I hang much less material. Blundering undefended pieces is a symptom of weak calculation and visualisation so look into how you can strengthen these. IMO puzzles done the right way is better than playing chess for this. In most sports, people dont improve quickly by playing their sport, they isolate and train specific skills. Chess is no different.

Thanks for the tips, where can i find the good calculation puzzles since the ones on my main site are the quick ones 

I use the rated puzzles on here. Ignore the clock. Just aim to get them correct first time. So solve in your head before making any moves. At low rating it is simple pattern recognition, but if you keep getting them right first time your rating will rise and the engine will give you harder puzzles were you need to calculate and find the best moves. You'll be calculating mating attacks and accounting for escape squares and defensive resource to get the move order right. Given time this will transfer into your game and you'll hang less material because you'll spot the problems several moves ahead.