The best way to deal with latex paint drips is to avoid producing them in the first place -- and proper paint consistency and technique can help you do that. When you notice a drip developing, you can usually nip it in the bud with your paintbrush or roller, but if it hardens, you may have to do some finish repair. Scrape or sand the drip and, if necessary, touch up the spot with fresh paint.
It's fairly common for drips to occur when you're rolling a wall or some other flat surface -- the paint oozes out from the edge of the roller and creates a thick line of paint on the wall. These disappear when you roll over them after your roller has been depleted and it's time to reload it. If you miss one or two, flatten the drips with a paintbrush, and then roll over the brush marks. If you don't notice a drip until the paint has stiffened, you may have to brush vigorously, reload your roller and roll over the affected area.
Drips from Trim and Woodwork
Anyone who has ever painted a windowsill knows how easy it is to produce drips on the outside edge. It happens as paint collects on the edge of your brush and beads off. Removing these drips can be tricky even when they're wet, because the excess paint tends to spread out when you dab it and drip onto the floor or get onto surfaces you don't want to paint. The best time to handle these drips is just before you load your brush. Dab each drip with the tip of the brush -- not the edge -- and scrape the paint into your container, and then stroke over the area with the empty brush.
Scraping Hardened Drips
You might not notice some drips until after the paint has dried and they're too hard to remove with a paintbrush. The neatest, most efficient way to remove a hardened drip is to scrape it off with a razor scraper. Keep the handle of the scraper low with respect to the surface, and scrape gently. Remove the drip in successive passes; if you try to scrape it off all at once, you'll probably damage the surrounding paint. Once you've leveled the drip, you may notice that the paint is darker than the surrounding paint. That's usually because it's still fresh -- wait a few hours, and the colors should blend.
Sanding Hardened Drips
Sanding drips doesn't produce the smooth results that scraping does, but it's faster, and if the paint has cured, sanding is easier. Use 150-grit or finer wet/dry sandpaper to avoid deeply scratching the paint, and moisten the sandpaper with water to lubricate it. Wrap the sandpaper around a block of wood and use moderate pressure on the drip to wear it away slowly. Stop sanding as soon as the sandpaper contacts the painted surface; if you sanded carefully, the surrounding paint should be unscuffed. It isn't a disaster if you rough up the paint, though, as long as you have some fresh paint of the same color for touching up.