Resin help, but also actually packing the bowl as opposed to sticking the entire bud in it and just lighting makes a big difference. Tear a bigger piece of weed an wedge it to the sides of the bowl, right over the whole, so it completely blocks it. Then just pack weed on top of it. Towards the end of the bowl, just suck lightly, so if it drops you can stop sucking before it comes flying down your throat. Also, if its towards the end and its ashy, blow across the top, not into but across (this will remove ash but leave good bud which is heavier, in the bowl), it might not even be worth hitting if its all ash.

Also screens suck, because you resin gets split up. When you don't use a screen all the resin goes to the bowl, which provides for better hits when toking actual bud, and keeps everything together when you clean you bowl, and want to smoke the resin itself.