For the most part, herbs are bushy by nature. Thyme, Oregano, Sage, Mint, Tarragon follow this pattern. Trim off what you need, and with good care, they will carry on.
Parsley and Cilantro grow from a corm. Which means that, like celery, the new leaves always come from the middle of the existing leaves. When harvesting these varieties, you can cut them within an inch or so of the soil line and they will keep on growing.
Rosemary and Lavender are actually shrubs, and will develop a woody bark. Keeping this in mind when trimming them will help you decide where to cut. From a purely aestetic point of view if you trim them a little from each branch, they will maintain a nice shape over their lifetime. Rather than removing an entire branch.
And that leaves the star of the show, Basil. It's natural tendency is to grow straight up and then produce a flower. By cutting it just above a leaf node, you will encourage bushy growth. By all means, if you only need a leaf or 2, simply pluck them off. As a rule of thumb, though, cutting it at a leaf node will increase your production and extend it's life.
As with all growing things, the hotter and sunnier the weather, the faster they will grow back.
The photos below show how to cut back mint. The same principal of cutting the stem just above a leaf node applies to most varieties. Basil, rosemary, sage, mint, lemon balm. tarragon. Thyme, and oregano follow the same guidelines, but the leaf nodes are much closer together, so you can simply give them a "hair cut".
Chives, parsley, and cilantro all grow in such way as to be able to cut them back, leaving a stump of aprox. 2" and they will grow back in a beautiful, lush way.
To trim basil, follow the same principal as with the mint. Cut the stem above any leaf node. This will promote bushy growth, and slow bolting (producing a flower then seed). If you only ever pinch the leaves, you will end up with a tall bald stem with a tuft on top.