Aim for 18 wins, any more than that is gravy. Weekend League isnt like any other mode on fifa, theres no trying new stuff out, play your game that got you there. Theres 40 games and a shit ton of rewards to gain, people will play the worst type of football against you, unnecessary posession, shielding in the corner and playing ultra d after going 1 goal up all in order to get that 1 extra win. It will test you, and you will hate it, but you will want to do it all over again when 5 of your defeats are to eaids goals or penalties and you realise how big a jump there is for next level rewards, and how close you were to getting them.
Learn from your losses, actually learn. Most fifa players in WL play the same way, so if one person scores a certain type of goal then everyone will score that same goal on you. Watch game clips of your conceded goals and see if you can pinpoint the mistake you made (99% of goals are from a mistake we make, stepping up or back with the defender mostly). Take breaks after an intense game (win or lose) and step away for a bit after a few games lost in a row so you dont fall into a slump.