Ohh boy... Ok well first of all I suggest getting here early and treat it like the DMV. They open at 8:30am M - F and according to the employee I talked to inside they always have a line. If you don't get here first thing in the morning and need to meet with one of their tax people plan on being here for at least a couple hours.
Also, Parking is $3 per 1/2 hour! There is no other close resource for a parking spot, but I bit the bullet anyway and used a meter downtown just a block off Freemont street. You'll need $2 in change for 2 hours and that was the max the meter I used would go to. But it beat the almost $20 parking in the building would cost me. So long as I make it back to my car within 2 hours and don't get a parking ticket. It was still a couple block walk back to the building but I needed the exercise anyway.
When you get here get inline to get a ticket. They give out tickets with numbers corresponding to your problem, then take a seat and wait. Also although they do not close until 4:30 pm, they are known to stop giving out tickets as early as 1:30 pm, which means you will have to come back another day.
So to sum up, Get here early like 8 am, park a few blocks away and save some money on your parking and don't fall behind on your Taxes!!!