Depending on the store (it's not like there's an industry standard for B&M's), you might walk in to a den of subohming cool kids who've got vapor clouds filling the room to your knees. They're into the extreme vaping scene and can be off-putting. Just look right past them - they're the equivalent of the car tuner street racers.
They should have a bit of a juice bar set up so you can taste a variety of juices. This is probably the best thing about B&M's - hands on with the most subjective part of vaping. Try as many as you can - like wine or food, it's a deep subject you should take your time with.
Gear is the other reason to visit a B&M - it's a great way to get see devices and tanks in the flesh... er, metal and glass. Don't be intimidated by all the choices - they're likely catering to a wide variety of vapers. Ask a lot of questions. There are no dumb ones. This activity has only existed for about 7 years. Even the most advanced vapers are, like, 2 years in, so it's not like they have a "lifetime" of experience to lord over you.
Now, the biggest issue with B&M's is the pricing. They have overhead (rent, utilities, staff, material costs) and charge more than any online vendor for the same products. It's completely understandable - by and large they're not gouging. My rule of thumb is: if they helped me, I buy there... once. If I can find that product online, I do that after the initial purchase. That's my rule. You'll have yours.
