3 simple rules
Rule #1: Always ALWAYS
read and honor the datasheet
Rule #2: Trust but verify someone else's design unless it comes from a manufacturers datasheet
Rule #3: Always question: "Why did some person do this in this design?"
Regarding #1: The best way to start understanding datasheets is to read them yourself. The more you read them... the more they stop seeming like gibberish.
Regarding #2: Just because you can find an example "on the internet" doesn't not make it right or "best practice". Having a circuit work "most of the time" should never be an end goal. A good design is one that was created to work under all reasonably possible conditions.
Regarding #3: If you are not questioning why a designer did something, you are not learning... BUT
sometimes hearing the "because we said so
" is the easiest answer from the more experienced.
Final note: It's always a good idea to learn HOW components work. Here is an example of why you want capacitors across your regulated supply voltage... (including the one at your regulator) http://www.thebox.myzen.co.uk/Tutorial/De-coupling.html