I've recommended JMO's video's many times. They are a fantastic learning tool from one of the best in the biz.
The best way is to learn by doing. A script is, in essence, a programmed series of steps, and most script steps are pretty much self-explanatory (give or take a bit of mumbo jumbo in some of the syntax). So try creating a script to replicate something you now do manually. Here is an example: you want to find a subset of records—
1. You go to a particular layout where you want to see the records you will find
2. You switch to Find mode
3. You enter your search criteria in the field(s) you want to search
4. You perform the Find
Try turning that into a script.