One of the biggest complaints that photographers have about using manual focus is that it takes so much more time to use than the auto focus. However, there's some easy tips to speed up the process somewhat.
Guesstimate the distance between the lens and the object upon which you want to focus. This will give you a good idea of where to meter your shot and take some of the fiddling out of the focusing process.
If you'll be trying to focus on something quickly, then it might be a good idea to try prefocusing your shot as well. This could mean simply focusing on something that's about the same distance away as your subject, for instance, the leaf upon which an ant is crawling.
Another possibility is to use auto focus in junction with a manual focus to get you in the ballpark of where you need to be. So, the auto focus can get you roughly where you need to be, while the manual focus can fine tune the shot.