Practicing on bots is a good idea if you want to learn what some heroes can do, but ultimately will be annoying. Because bots cheat. Zeus likes to killsteal with his ultimate, even if he cannot see you farming in the forest, he will use it when you are low enough to die, they react faster than any human being when it comes to stunning you as your BKB runs out, and are fairly predictable overall.

Sharpening your claws into some other pubsters is the fastest way to gain actual skill in the game since they are unpredictable, make mistakes, they are humans (though you might debate it on a case by case basis).