First up, I wouldn't say that being killed a few times makes you a 'rubbish player'. I am level 183, have done a lot more PVP recently, but two days ago I had a scuffle with a level 18. I killed him twice, he killed me once. There are lots of variables on the day.
Others have made some great points, but I'd add that your general health and stamina are also relevant. I swim and fish a lot and my general health and stamina are wildly better than they were when I started out. In a pitched battle both of those stats can really help. Lower level players seem to love choking (!), I'm often in Valentine and one will come up behind me and get me in a headlock. A couple of months ago I'd die, whereas now I can almost always break free and reverse it, or have time to draw a weapon despite being hurt. That's as much down to greater health stats as anything else.
In terms of loadout, I carry twin navies, an Evan repeater and a Rolling Block when it comes to PVP. I switch my weapons to that loadout specifically for it (otherwise I generally have twin volcanics (working on the 1000 kills achievement), a varmint rifle and a Springfield (both for hunting). I also swap out my ability cards - Never Without One III, and then also the one which favours twin handguns. At level III it's really powerful. Doesn't feel that authentic, but if they're griefing, they're getting it. I also carry a cleaver as it's great in close and you can chuck it (and there's an achievement). If someone is hurting me up close, as @Vendetta said, I favour opening up some distance. Then take a ridge or high ground and pick them off with the Rolling Block. @Vendetta and I dress alike and play alike!
But really it is just practice, practice, practice. I'm far from the best but can hold my own against most and don't consider myself a high end gamer. I love the game for hunting, fishing and general moseying around. PVP can be fun but isn't my aim but it is possible to get much better at it. A little while back I thought of myself as cannon fodder, but it does improve.
o7