How to become a contemporary art collector?

I see art work in the gallery. I curious how to collect art work which made of new medias. How to buy? How to select? and so on.Thank you.

Buy what you like and what you can afford.
Galleries usually have a book when you go into them that list the art and prices. Some galleries even have open nights,it depends on your city, Philadelphia is every first Friday in olde city, they have receptions,wine and cheese and you can view the art meet the artists and look and see if you want to buy an thing.

Collecting art becomes an extremely expensive exercise! If you purchase new artists, and be selective in doing so, you might find something very exciting.
Many new artists begin by exhibiting their paintings at weekend markets.
If you want to learn how to collect you should take a short course in Fine Arts - this will teach you what you should be looking for. You don't have to go to Uni or TAFE. There are many Community Colleges which do this.
My philosphy is, you buy what you like, as you may have to live with it for a long time.
Good luck.

I don't know what "new media" you mean, but whatever the medium, you should consider permanence and practical issues of storage and display. Regarding what you purchase, you could buy whatever you enjoy without regard to the opinion of critics or other "experts, but this could be expensive in the long run. I believe it's better to be guided by critics or other experts who have no vested interest in the sale of the work. Most collectors say that the purpose of collecting is to gain knowledge of the field as well as enjoyment, so either way, you need to learn a lot about the artists and works you're collecting.

Works of art may be purchased from galleries or other collectors, and occasionally from artists, though if they have gallery representation, it's usually discouraged by the gallery.

More specific information would be helpful.

http://www.artinfo.com/ read the articles on collecting in the archive of Art info. Get a certificate in art appraisal. Read Dave Hickey and Lane Relyea.

Here is a basis library that can get you started.