Comment below rating threshold, click here to show it.
Step 1 - If you have never played a ranked game, you should start "unranked" instead of starting at 1200. You would have to play 15-20+ games in order to be placed at an ELO based off of where your ELO would be had you started at 1200. This keeps people out of the 1200 range if they don't belong and might make it a little easier on the people that have struggled in the 1200 range to not get feeders that belong at the 900 range.
Step 2 - If you had a leaver on your team and you lost, you should only lose a portion of your ELO instead of the full amount. Penalties would have to be much greater on leavers for this to be effective without tampering, but it sucks losing the full amount of ELO because somebody quit at level 3.
Step 3 - If you had a leaver on your team and you won, you should gain more than the normal amount of ELO. A 4v5 is a much harder fought victory and thus should be rewarded as such. This would encourage teammates to not surrender at the 25 minute mark just because you've lost 2 turrets and are down by 5 kills.
*Step 2 and Step 3 should only apply if the leaver left at least 5 minutes before the game ended to avoid tampering.
Step 4 - Any leaver should be penalized much more severely for each leave after their 1st leave. Take away 3 losses worth of ELO or even ban them from ranked play for a x amount of time after y number of leaves. Leavers need to be penalized so harshly that people only want to leave when legit, real life stuff happens (which should be very rarely).
These are just my thoughts on the topic while sitting here bored at work. Thanks for reading.