the first thing to remember is not to buy her clothes because there might be a lot of problems with sizes and comfort. some stuff might look adorable but when you wear it that might cause a lot of pain and stress for the body so in these cases it is better to go shopping with her. the same is better do with such a piece of jewelry as rings. you have to know exactly what the size of her finger or otherwise you will have to bring the ring back after it does not fit her.
making a good gift will be much easier when you will consider her interests 