@CO2000A_ABest thing you can do is find some people who post good numbers and practice with them in the firing range. If you get paired with a predator or diamond player ask if they will help you. If you can't find help, turn the dummies on in the firing range (you can find videos of how on youtube).
What legends are you picking? Gibi is an alright choice for a beginner. Mostly because he takes more damage than other legends. Bang is not a bad choice either. If you use bang keep in mind people can see in the smoke so it's not 100% effective. Her abilities are really geared towards disorientation. Disorient the enemy with her tactical/passive and use it to your advantage.
Guns flatline is probably a decent choice. Spitfire is not bad either, especially if your aim is not that great you'll have a huge magazine and plenty of bullets to fire if you miss shots.
Top guns are the prowler with a select fire, 99 with a magazine on it, The 99 is hard to use because its high recoil and high fire rate. You really can't miss any shots with it or you'll be dead. So it's something you might toy with in the firing range and rounds when you want to try something new.
Map rotation is key, movement is key.. If you just stand still while shooting at enemies you're going to get killed by people who can strafe or crouch spam. Map rotation is hard to explain and is something you just have to learn. Some areas are going to be choke points and high traffic areas with intense fights. Those areas can change depending on where the drop ship goes, where people drop and where ring is.
If you have any specific questions just ask. Forum members here love to help out other players.