Whether it is new or old some painting preparation will be required, some kind of spackle or filling compound will be required to fill the cracks, holes and other imperfections prior to you starting painting.
There are a number of products available to do the job required and here are the most widely used:-
1. Plaster / fillers- these are used mainly for the filling of cracks and joints in drywall/plaster work as well as small holes
2. Putty is used mainly for filling of nail holes etc
3. Caulk fillers; filling of gaps and joins between substrates
4. Heavy fillers are used for filling larger holes (also known as Builders bog)
All fillers have special jobs to do so make sure you choose the right filler for the project.