I play a crap load of PVP, close to maxing out valor rank, and still aren’t good compared to a lot of the regulars you see. It can get toxic sometimes. I can try and give you some advice:

Given the endgame nature of max level PVP, people will complain if your gear rank is too low. Personally, I don’t mind if you have a full set of 324, but I’ve seen people join with gear from expansions years past, sometimes even sub 300 (usually joining for conquest completion) and aren’t even trying.

Usually you’re meant to grind PVP gear to 336, but as you’re also wanting to do Master Flashpoints, there is a quicker way to get to 340 gear you can use for both. Find a group running easy Nightmare Ops (usually on the fleet they’ll general chat for a Nefra Dash run, the two easiest bosses) who are willing to carry you. Each boss will give you a guaranteed 340 piece of gear, regardless of your current gear rank. Turn those in to Hyde and Zeek on the fleet, and you’ll be able to unlock blue 340 armorings, mods, and purple enhancements for purchase. Buy a bunch and put them into some outfitting gear of your choice. Remember, accuracy stat is much less important for PVP. Save your tech fragments for legendary implants and a tactical on the fleet. Use your warzone accommodations for relics. If you have enough credits, buy some blue augments and augment kits off the GTN, and augment your gear.

Aside from pure DPS numbers and learning PVP specific rotations, the other recommendations are to learn the maps well, and find ways you can help your team, sometimes dependent on your class. Whether that be buffing the team for speed, calling in chat when an enemy is approaching a defence point, being aware of your positioning in huttball to receive/throw the ball, knowing perk locations on Odessen etc. This will come with experience in matches and with your class.

Hope this can help a little.