Here's an obvious but often forgotten trick: Like they've told you, if you are going to manually put an address, always copy paste it, but always, always, double click on it so it selects the entire string of characters without leaving a black space. I actually don't know what would happen if you put an address with a blank space at the end, but just in case, be sure that you don't leave any.
All Bitcoin addresses have a built in checksum so it is almost impossible to type them in wrong. If you change the address by leaving out a character, adding a character or entering a wrong character it will not be a valid Bitcoin address and it will be rejected.
Having said that it is always more convenient to use a QR code or copy/paste than type in the address - but I have typed them in a pinch.
