When I first started learning Perl, the first thing the guy who introduced me to it drummed into my head is:

Rule 1: "Every Perl program you ever write will use warnings and strict."
Rule 2: "Refer to rule 1."

As a beginner, I think this was absolutely the best advice I could have been given.
Although I now understand that there are the odd times that you can get away without them, I still always do it out of habit and I'm yet to encounter a situation where it makes (more) sense to not use them.

--Darren