Crawling
My son crawls since he was 6 months old. I thought I should share my experience:
1. Baby is more willing to learn crawling if he falls, it won't hurt that much. I noticed this as he crawls a lot when at Infant care, as the floor is carpeted, so even if he falls, it's okay. But at home, he crawls less, as it's coarse tile floor, and it hurts a big deal. So providing a appropriate environment is important. Bed is good, but the soft type, and have to watch him carefully (not to fall off bed).
2. put his favourite toy in front of him, not too far away, to where he is just about to touch it, so to encourage him to move his body. When he just about to touch it, move it further, repeat this a few times, and finally let him play with it at sitting or lying down position. Can also try with something new that he never play with, don't have to be a toy, like can drink, tissue box, anything that is safe for baby to touch/play and may interest him, or he always look at when you use it.
3. Crawl together with your baby. When he sees you on the same level as him, he is more willing to be on tummy and try to crawl.
4. Don't force him if he doesn't like it. Let him sit up for a while and play. Then try to put him on tummy again.
Hope this helps a little!