LP Splash In Ranked Promos
So I just ran the first couple of matches for my ranked play this season and already noticed that my wins in other roles splash LP onto the roles I've already done at least one placement match in, and that there's no negative LP splash during placements.
So what does this mean?
Whatever role you want to have your highest placement rank in should be the first role you play your placements in, but only for one game. After that, you should unlock all five roles so that all five can benefit from the splash LP. Spread out your games over your four non-main roles, and try to nail as many wins as possible. Don't play your eighth and final placement match in any one role until you've reached your seventh placement match in all of them. This includes your main role, though you shouldn't start playing games in that role until all of the other roles are up to seven.
From there, you can play your final placements in your four non-main roles and cap it off with your final match in your main role. Even if you only pull a 50% win ratio over the 32 placement matches that aren't for your main role, you'll still splash enough free LP onto your main role to easily go up a couple of divisions in your placements.
Happy hunting, Summoners!