Razors won't work well on a regular length hair--at least not with any ease or speed. Other posts in the past give aspects of the following advice, which I'm sure someone will amplify on and improve.
First, the hair needs to be buzzed very short with electric hair clippers (the barber would do this, too). Clippers w/o a "guard." If you have no clippers, buy a pair. You might say, "Why spend money on something I'll use once?" Well, you will have them should you shuttle between hair and sly in the future. I found my pair a useful investment. So, clippers, and this will leave you with hair only a millimeter or so long. Do this over a newspaper and in front of a mirror, and get the neck, too (a hand mirror is a big help). THEN you need to think "razor."
But hydrate that hair first! Shower and shampoo thoroughly. With hair softened, what follows is just what I do when I go from "some hair" to sly. I lather with almost any shaving cream (some swear by gels, but I find cheap foam works OK for me)--not thickly, just put some on the palm of the hand and smear it all over the dome. Then, to save money by not using a high-tech blade for what is basically prep work for the future, I sacrifice one or two disposable razors with the first passes. Take it slow, a few square inches at a time, rinsing the blade after each pass. I shave m.o.l. against the grain first pass. Then, I lather a second time and use the first razor a second time, or the second razor the first. And shave again. Wipe the head clean and with your hand feel for spots that still feel rough, and touch up with as many (un-lathered) passes as needed to produce what smoothness you want (or can get). Throw out the disposables and get one of the regular razors sly guys recommend on various posts for future shaving.
I have, however, said in the past that most razors will produce relatively OK results unless you are hypercritical about matters, but I won't get into debates about "My razor is better than your razor, nyah, nyah!"
You might move even to the next stage, once you achieve sly, and put a nice shine on the dome with one of the HeadLube products--I use "Glossy" and I glitter in the sun.
