The most difficult parts of the application are the parts you do not have control over. The letters of recommendation are one of the most important parts of the application because it shows how other people have influenced your work and how they feel about your abilities. To get a good set of letters of recommendation you need to find a diverse cross-section of professionals and academics. Professors are always going to be your best bet, but if someone is an esteemed film or video professional they will be helpful as well. Hopefully you will have worked on several extracurricular activities or internships in your time as an undergraduate, so professionals involved in these can help quite a bit. If you took part in film events or other art related organizations then these are good places to look as well.
Every school has different numbers of letters they require, but it is usually two to three. Go ahead and try to get four to be safe, especially since it cannot really hurt to send more than is asked for. You may want to contact possible recommenders by email ahead of time. This gives you a chance to give them updated information, such as a resume, filmography, and maybe links to more recent work that you have put to an online venue. Make sure that they are able to reference specifics in your work, so it is best if they have been intimately involved in your filmmaking or artistic process.
Many schools now ask for an online recommendation process, which can complicate things further. Ask them to write the base letter of recommendation, but have each copy addressed specifically to each school. From here you can get some in physical form from them to send to the institutions and then the other ones can be submitted online according to the specifications of the schools’ website. Usually you can opt to send all of the letters to the school on your own in physical form, which makes things much easier. All letters that you do get in physical form you need to make sure that the envelope is sealed and the initials of the author should be written over the seal.