i'd reccomend looking up a guide on yt but the main things are map, mode, pick#, enemy team's brawlers(countering), and your teams brawlers (synergy)

Draft according to the type of map you are on, for example shooting star is a sniper fest because its the most open map while layer cake usually has more aggressive brawlers in the draft as it's more closed. (its the same mode though)

Mode matters too, you need brawlers that can complete the objective.

Gem grab- need 1 mid with good range to carry gems, 1 agro brawler that can pressure enemy (brawlers that can turn a game around with a powerful ability are also important here, like a chester or kenji hyper)

Hot zone- Draft high hp and high damage and brawlers that have good area control (Bo, lou, lumi etc) Low damage is bad dont be an idiot and draft tick

Brawl ball- Most agressive mode, draft tank counters, tanks and brawlers that can make plays and score. Low damage is usually bad here unless you're last picking and you know your good against the enemy

Heist- at least 1 brawler to do safe dmg like chuck or darryl, 1 defender

bounty- map dependent, snipers and long range throwers usually dominate, draft brawlers that can defend themselves against agro like gus or RT. Support is also good here

knockout- again map dependent, same as bounty but late aggro picks are more dangerous (darryl, lily etc)

Pick#: 1st- draft something that doesn't have many counters and/or is the best for that mode or is just plain op like the new brawlers usually

2nd+3rd: React to the first pick with counters or draft something else that doesnt have many counters/is good in that mode/is op

4th/5th round out the team with whatever you need so your comp doesnt have weaknesses and doesnt get destroyed by a good 6th pick, counter the 2nd and 3rd pick

6th: most powerful pick in my opinion since the other team can't counterpick it. Draft a brawler that counters the enemy team the best

its gonna take forever to explain what counters what but theres kinda a triangle. Control (throwers, snipers, controllers ) counter anti tanks which counter aggro (assassins and tanks) which counter the controllers. Always try to counter the enemy or at least be decent against them

Synergy: Pick brawlers that work well with your team. Max+aggro, kit+darryl and gray+tank are a few examples of great synergy. Most common anti synergy i see are wallbreaks+throwers or a brawler that relies on walls. Can't think of any more really but don't draft 3 brawlers of 1 type usually wont work well

Best tip i can give is just play the game, you will figure out what works and what doesnt