It is my perception that there are two versions of microjumping;
1. In-system micrjumping is when you attempt to reach another loaction, within the same system, by taking a short trip to hyperspace, like Derrik said.
2. Out of system microjumping is if you, as an example, exit hyperspace into galactic position (10, 10), system position (19, 19), aka lower right corner. If your ship has a very low sublight, and the in-system destination is (8, 8), you will use many hours to reach it from (19, 19). In this case you can hyper over to glactic position (9, 11), and then hyper back to (10, 10) once more, this time appearing at in-system coordinates (0, 0), which is a bit closer to (8, 8) than (19, 19) is.
Option 2 is somewhat HS level dependent, in that a ship with HS 3 and sublight 20 will save more time than a ship with HS 2 and sublight 20. Ships with low HS and high sublight don't have much to gain with this technique.