I want to be a Mohel.
I learned the Tur - Shulchan Aruch (YD 260-266).
What should be my next step?
P.S. I live in Brooklyn.
Probably the best option is to learn from a mohel or get good advice from a good mohel. The best and most friendliest Mohel I know is Rav Paysach Krohn, this web site has his number and email. I know that he's busy doing britot and lecturing, but, at worst, if he can't train you, I'm quite certain he will advise and, if appropriate, recommend you to the right person. (He may also try to sell you one of his many books. At least you may get them autographed :-)
Another possibility is to contact his son in law, Rav Ephra'im Perlstein, who is also a mohel, info here.
If you do, eventually become a mohel, I may ask you for some "tips" :-( :-(
My brother in law who became a Mohel apprenticed for a while with a Mohel who was doing it for many years. When the Mohel was confident in his abilities he gave him the go ahead to do it on his own.
I have also heard that many times a new Mohel after apprenticing begins by doing a Bris on his own child.
I am pretty certain that most Mohelim begin this way.