Discipline for a 10 month old

CurtsWife

My first baby is 10 months old (2nd one on the way!) and we have two major problems right now:

1. screaming at the top of her lungs for no apparent reason 
2. continuing a bad behavior when I tell her no, until I get up to go to her then she falls on her butt giggling
   

I know she is just starting to understand language, but I do sense that she knows when I do not want her to do something. She always turns around and gives me the biggest grin when she knows she is in trouble.  I know I have to be consistent with her, but this 2nd pregnancy is kicking my butt and I am getting way more frustrated with her than I should.  The round ligament pain always seems to kick in right when I need to stop a behavior.   

 What tricks have you found to help your baby understand what is acceptable?