Hi! I've only learned to crochet in the last month and have made a baby blanket all in trebles with a few colour changes, so nothing too adventurous!
It needs finishing and my MiL suggested a scallop/shell edging. She taught me crochet so I trust her advice.
So, I finished the body of the blanket last night, but I'm not sure where to start on the edging. 
Should I do a round of doubles all along the edges first to pull it all together?
Will the repeated trebles affect the edge, as the stitches already have a sort of wavy thing going on? Will I need to fill them in somehow?
How do I go round corners?
I am a true beginner, I can only do double and treble, I'll be learning this shell stitch as I go along.
MiL isn't about today so I can't ask her, plus I think it will be nice to get some help from the very experienced people on here.
Please help, if you can!