What do I need to look for in an area for the first fortress?
if this is your first fortress, I would suggest finding an area that matches the following conditions:
This should lead to a biome that satisfies the following conditions:
Ensure there is at least one white ground layer in the overview, and there are no layers which have blue squigly lines (aquifer indicator) behind them, and the name of the river of brook is given. (a brook is preferred and stay away from the sea)
Also, if there are Goblins around, check if they're not at war (Tab)
whle these settings aren't a source of much fun, they're perfect for learning the first steps in dwarf fortress (the only fun thing you can basically do, is flooding your fortress)
This list isn't exhaustive and usually can be answered by the question: What would be the most fun?
Now if you're new to the game there are a couple things you should keep an eye out for:
After your first couple fortresses, you'll want to start ignoring everything on that list above (or go the other way). Its all just more fun!