It's best to be right at the Equator for a launch to Geostationary Orbit.
You also launch east to get some of earth's rotational speed.
When launching, the orbital plane's inclination will be the degree of latitude or more. With a 0° latitude, you can pick your inclination - 0° in this case. This saves very costly changes to the inclination (among the most rocket fuel consuming maneuvers. For reference, since Russia is really high in the north, they need a whole additional rocket stage just to change the inclination).
Since you want to launch east, you'll need some empty space in that direction, since people get mad if you launch over their territory and your launch fails.
Best places to launch are places like:
East coast of Brazil, near Macapá
Southern Somalia, around Jamaame
Both are at the equator and have a lot of empty ocean east of them. For political reasons I'd prefer Brazil.
Probably the best existing space port would be Kourou in French Guiana, the ESA's "best" spaceport.