Like Susie said (and for anyone else reading) the emotions and trust play a big part of things. Unless you use excellent knots, or other devices like leather/metal restraints, the person is going to be able to escape. That is not necessarily a bad thing. For it is more a mental condition of the feeling of being helpless, than a physical one for many.
Heck, some people even love the feeling of being made to keep your hands over your head, or spreading your legs. It is a vulnerable position.
And it depends on what the person tied wants to feel: vulnerable, taken, pleasured against their will, or even pain.
So, learn some knots (many nautical or scout online sites, "Two Knotty Boys" for advanced stuff), find something to tie with (rope, straps, scarves, business ties - just be careful that scarves don't become too tight), set aside some time and have some fun.
The most important part is to communicate - your safety feelings, how it felt to be controlled, how it felt to do the tying, and any concerns you have during or after. It can bring you closer.