For Michael there was this elephant shape sorted toy that he loved, but he loved it empty. Every time we put the shapes in he would immediately bang on it's nose where the shapes came out until they were all on the floor. So we started putting it just a bit out of his reach and he learned to crawl towards it to satisfy his OCD about it.
For Jon, nothing was more enticing than a tower of blocks he could knock down. We built the tower just a bit in front of him and he instantly figured out how to crawl to get to it.
We have been working for weeks to find that special object or person that would get Becca to try crawling forward, and yesterday I finally found it - her snugglie! Let me tell you that it required a lot of enticing though. She is so good at getting where she wants through rolling. She saw me holding the snugglie. She rolled once over and back and looked up to eye the prize again. Rolled over and back again and again, each time rotating herself a bit until she was sideways. Then she rolled and rolled across the room to me and the object of her desire. So I had to get more tricky. I had to keep moving the snugglie to be right in front of her after each roll. After some fussing about it, she finally crawled forward and grabbed it from my hands. We knew she could do it!