Need advice before doing Placements

So I am a bit confused as what to do atm. My main account I had for 4 yrs now that I never really did much Ranked play on, I took lots of time to learn all the toons, who they counter, how they are countered. Must of played a couple thousand games in Qm and Unranked with many wins and losses.

This past season I wanted to start getting more into SL to take ranked play more serious. Did my 3 placement matches, 2 wins 1 loss and got placed in Bronze 5. I accepted it for what it was, even tho I play around the Plat level skill wise. I didnt complain because I knew I could just climb if I just did a lot of Soaking / camps in the beginning and didnt do dumb things during obj or team fights.

Problem: I only got around 25 rank pts per win / loss. From the position I was placed in B5 it would take me about 45 wins in a row to get to B4. At the end of the season I was about 80% through B5. Never got close.

So I am asking for REAL ADVICE. I have not yet done my placement matches this season. Was reluctant to do so before I asked our higher ranked community for help.

Any players that you enjoyed playing with or you had good teamwork with, always add them and invite them to groups, never solo que if possible but never have more than a 4 man premade, makes for easier match making and more consistant games.