There are a couple knots that you'll want to familiarize yourself with. These will help you knot everything on launch day. The first knot is called the Double Fisherman's knot. This helps for joining the balloon to the top of the parachute, and any other ropes that need to be joined. It is almost imposible to untie, and thats why we used it in our project. This video below shows you how to tie the double fisherman knot. It's pretty simple, and you can probably master it with a couple practices.
The other knot you'll want to know is the box sling. This is the knot that goes around the payload box, and connects it to the main flight string by a double fisherman knot. http://notableknotindex.webs.com/boxsling.html