Sewing them in is pretty easy actually. For dreads that have loops on them, just pull the loop out until its hanging free. Take that hair and palmroll it. Then stick it through the eye of a large sturdy needle. Sew it straight down into the dread. If it is too long just do it again.
Crocheting is a good start for some heavier duty dreads but it causes the hair to not dread if they are still young, causing weak spots. You can combine dreads at the base using a crochet hook and the sewing method. Or get a small Phillips head screwdriver and make a tunnel in the dread, starting at the base. Then thread the dread into the other one with the sewing needle. Its tricky but it works.
I used these two methods to achieve awesome professional looking dreads. Started with 106 and ended with 80. Getting a touch up helps a lot. Doing a deep clean every 6 months or so can pull out all the nasty shit that piles up and it tightens them up a bit too. I did a deep clean after every touch up to lock it all in.