Assuming it is the same for all LEAs - if you weren't allocated your first choice you will automatically get put on the waiting list for any schools that were higher preference than the one you were allocated. When spaces come up at those schools, they will offer to however is top of the waiting list, irrespective of whether that person has accepted or rejected their allocated place.
Accepting/rejecting your allocated school will have no influence on whether you are offered a place at a higher preference school, so my recommendation is to accept the place so that you at least have one. The wait list is horrible as you can move up and down it, as new people can be added to the list and are placed in order of their child's eligibility for the school. So if someone moves in next door to you tomorrow and their house is slightly closer, and they ask for their child to go on the wait list, they could be placed above your child (assuming there are no critieria that trump the other child, such as sibling etc).
No one ever wants to hear this, and I didn't at the time, but my son got our 4th place for secondary, and we were gutted. Now we actually feel it was the best choice for him, as our experience of the school has been so positive, and we know friends of his who were allocated first choice, and the school everyone wants their child to attend, and two are rarely in school and the other has been deregistered to home school, so the school you think is best doesn't always pan out to be.
Good luck with the wait list though. You can go onto the wait list of other schools that you didn't originally choose, if there are any suitable.