Some people are difficult to buy gifts for, you will end up spending a lot of time wandering around shops desperately trying to find something to buy.
It is always wise to create a little brainstorming list of things that the person likes, or memories you have of them, perhaps places they have been, things you have done together and things that they have mentioned in the past. These are good indications for gifts that people will enjoy.
Sometimes it is an indication of how well you know someone if you really struggle to find a gift that you think will please them, if you know their hobbies and the things which they really enjoy then you should be able to come up with a few ideas. Of course for people who have hobbies they love but that you don't understand well, it can be difficult to have the expertise to buy something for them.