It took me 8 runs as my PMC/Player on Customs to achieve an extraction, so yeah I lost a lot of decent gear in that learning process. As a SCAV I've had much better luck. I'd say I make Extraction around 8/9 times out of 10. I just play it safe and try and avoid fights head-on as most other players I've encountered are really well geared, so there's no point in trying to take on squads as you'll just get outgunned/outnumbered/flanked pretty easily.
I do take on duos myself, as if you get the jump on them it can be pretty easy and fast to take down a few players who aren't sure of where you are. I just hang around and take the scraps off the dead bodies when no-one is around, loot the hidden lootspots hidden around the map and hug the fence-lines to get to the extraction point. Try and avoid being out in the open anywhere, and take it slowly.