...I guess it would be a good time to note that if you want two different colors, you should paint the entire wall one of the colors you want THEN put the tape up for your second color.
The next step isn't much fun either. It too, also takes time and patience. But this is the MOST important step and very crucial for super straight, clean lines once the tape comes off. This is especially important if your walls are textured. You can find a paintable caulking that is available at your local hardware store. Looks like this (you'll also need to purchase the apparatus to put the caulk in):
Follow the manufacturers instructions or ask the workers at your hardware store. I LOVE my local Home Depot, they are very friendly and helpful! Also factor in time to allow the caulking to dry per the instructions. It makes a HUGE difference.
Now for the fun part, painting! Make sure you paint every other line. A few rooms before this project I learned the hard way, that you MUST pull the tape off while the paint is still WET! Once the paint on the tape dries, it hardens and is difficult to pull off the wall. Additionally, it could pull off pieces of paint and ruin your hard work caulking.
Happy Painting!! xoxo