Assessing rental market availability

[Ignacio Rosenberg]

Merry Christmas everyone.

I'm brand new to investing in real estate and I hope to start next year in earnest.  In the meantime I'm learning and researching as much as I can.  I'm curious how you all determine availability in a market.  Where I'm stuck is I find areas with lots of rental units available which leads to great research, but then also worries me that if there's so many vacant units, wouldn't that be a sign about a bad market there?

Thoughts? How do you find the "sweet spot" for rental markets?