A search on Japanese rope bondage, Shibari, bondage and any other keywords will give you advice and ideas. Shibari/Japanese rope bondage may be a little advanced at the moment but is something to aspire to.

Not sure it is all that possible to learn anything complicated from an online resource. You may have to have someone show you how to do it.

A tip I learnt many years ago is to make sure you wrap the rope round the part of the body you are tying several times before you tie it off. That way you provide more support and have less chance of cutting off the circulation.

Also, I'd suggest getting proper bondage rope (I think it is made from silk fibres rather than hemp) from somewhere as this is specially made not to burn or rub like hemp or other fibres.

You may also want to look at something like bondage tape - a PVC tape which is stretchy and sticks to itself like cling film. I have found it a lot easier to tie someone up using this than rope.

Finally, it is actually easier to do bondage with leather cuffs so you may want to get your boy a set of ankle and wrist cuffs if you haven't already. You can then link these with chain or rope.