What kind of bike should my first bmx bike be and what qualities should it have?

A bmx and flatland bike are different from one another.

Flatland bikes are generally pretty heavy and allow precision moves on hard surfaces. They can develop a lot of inertia and usually have things like pegs and a Gyro, along with a front and rear brake. If you want to do tricks and plan to stay ON THE ROAD then you want a flatland. I strongly suggest you look at Diamondback- they are excellent bikes for the money.

A BMX bike tends to be very light (compared to a flatland), and have sealed or shielded bearings to avoid failures due to dirt and mud build-up. They should NEVER have pegs installed nor any kind of trick hardware. BMX is for dirt jumping and racing and makes the most out of the energy you use. They accelerate very quickly but have very little inertia to carry you. Depending on your size, BMX bikes often have different lengths...short, standard, XL to allow best fit for you. Again, I would suggest for your first BMX to look at Diamondback or DBR (Diamondback Racing), or perhaps a Specialized.

Whether you are a beginner or not, do NOT assume that a "cheap" bike will do. Expect to pay $250 or more.