Aim and shoot! As soon as you spawn, you need to be aiming with the Machine gun and shooting whoever is in your path. Chances are they may be low on health so you may be able to frag them easily with the machine gun. Have Guantlet readily available so in case you run out of ammo, you can easily get a frag using gauntlet. Always listen for sound queues of other players that are about to die. Most of my frags are done by pretty much stealing frags. Meaning when other people are fighting each other, that's when I attack and frag them both because they are low on health. Always watch your back, players will be everywhere! Listen for those sound queues of footsteps. (Headphones Recommended) Predict where your enemies are going to be. Shoot areas with rockets/grenades where you think players might be. My favorite spam weapons are Rocket Launcher, Grenade Launcher, and Rail gun. The Rocket Launcher and Rail gun are great long-range and short-range weapons. When enemies are close, switch to shotgun and get those up close shotty blasts! Switch it up and do Rocket/Rail gun combos. I do a lot of rocket, rail, shotgun/machine gun combos. The HMG or Heavy Machine gun is way better and does more damage than your starter machine gun. LG or Lightning Gun is probably the most common weapon to use if you want quick frags. I use it so much. Plasma gun, Chain gun, Nail Gun, and Mine Gun I rarely use.

Lastly, Know your maps good, Armor up and get Mega Health and Quad Damage as soon as you can, play like a mad man, and use a good Pro Config. Default config just does not help. I am using Evil's Config now and it is properly tuned to my liking. Makes FFA a breeze to play even with high ping. Not much to this guide, but it's how I play. Having a good computer helps too.

My PC Specs:
i7 7700 Intel CPU
Corsair 750W power supply
Asus ROG Maximus IX Hero Motherboard
16G Corsair Memory
EVGA Geforce 970 Video Card
Roccat Pyro Keyboard . Badass Keyboard by the way. Makes dodging shots a breeze. Here is link to video https://www.youtube.com/watch?v=QrdCHOcGouY
Razer Viper 8khz Mouse. Very Precise/Accurate mouse Edit: Using Steelseries Aerox 3 now. ( part of the problem why I am not a pro. I keep changing ♥♥♥♥ up. Stick with what you got. )
Razer Goliathus Control Extended mouse pad
Razer Blackshark V2 Pro Headset
And a BenQ Mobiuz 144hz gaming monitor

My Equipment may be old to some, but it's great for Quake Live.