if you are a normal civ with no UUs, and still want to go domination, my plan is usually something like this:
1) if pangea, basically wait. Play nice like a peaceful science game but with your target being artillery (dynamite) instead of spaceship parts. Artillery is a huge game changer, and usually results in swiftly defeating any nearby AI. Go to education, fill your university slots to ensure some great scientists, then switch to the bottom part of the tech tree. Use your great scientists to get to artillery ASAP. Have cannons ready to upgrade, and a few supporting units. Once you upgrade to artillery just start smashing armies & taking cities. It should be pretty straightforward...artillery outrange cities so all you have to do is defeat the field army, then cities are easy pickings. Take the capitals and raze most of the rest, depending on happiness. Get to an ideology ASAP to help with happiness.
Artillery should be good to conquer at least a few AIs. On lower levels, you can probably clear the entire pangea with artillery. But I like to circle back to the top of the tech tree (public schools & research labs) after I get dynamite, just in case. Often you will need the later units to finish off the last few AI (especially air force) so you don't want to completely neglect your science infrastructure.
2) for other map types, you have more options. If you share a small landmass with 1 or 2 other AI, you can just kill them with comp bows and be done with it, then build up for an eventual overseas invasion. The difference is that on pangea, you will get massive warmonger penalties for early attacks, because you have witnesses to your genocide. But if you kill everyone before you meet the other civs, they don't know about it, so there is no warmonger penalty. Because of this, the map type can play a big role in deciding when to attack.