I know most Apple Stores are crowded these days, but there *are* things you can do to alleviate the wait.
1. Don't shop from 12-5pm and 7pm-close on Saturday. There's usually a lull between 5ish and 7ish when people get dinner/catch a show, so if you MUST go shopping on a weekend, that's your "window."
2. Don't shop on Sunday. Period. This isn't a religious thing--after three years in retail, I can safely say that Sunday crowds are the worst. Sundays are busier in a different way than Saturdays; Sunday shoppers want lots of individual attention but are less likely to buy. This ties up employees in longer transactions, resulting in longer wait times for you.
3. When it comes to weekdays, Apple's website is right--shop early, shop late. Stores are busiest between noon and three (when people are on their lunch break) and tend to calm down quite a bit after 5. Beware: there may be a rush after 7pm, or there may not. Depends entirely on the day.
4. Be patient.

If you stress or worry about the environment, you're going to react poorly to it because you've already prepared for it to be a negative experience. This advice goes triple for the upcoming holiday season.
5. If everyone is with a customer, look around and see if you can discern who will be free next OR (better yet) find a transaction that looks similar to what you're after (buying an iPad? Find an iPad transaction. Looking to purchase the case in your hand? Queue up behind someone who's doing a similar quick transaction). Most of the time the staff is capable of handling your needs, sometimes by including you in their current conversation or by letting you know that they'll help you next.
6. When in doubt, tap someone on the shoulder and ASK where you can find help. So many people get frustrated because they don't get approached, but often times it's because we're so busy and we see SO many customers that we don't always notice YOU and your lost look. Be proactive! Just a simple, "hey, I know you're busy, but when you're done I'd like to ask you about X" or "can you point me in the direction of a cash register?" will suffice.
7. (and MOST importantly) PLEASE respect the staff. They're there to help you, and I can assure you that they're generally doing the best they can (ESPECIALLY in an Apple Store). Retail wages are not very high, and the employees put up with an inordinate amount of BS from shoppers who are downright cruel. In retail and food service, we are all human beings with feelings, and a little respect can go a LONG way. I was much more willing to bend over backwards for someone who respected me than someone who was rude.
These suggestions are derived simply from my work in retail rather than work specifically at Apple. No matter where I worked, these held true.
Happy shopping.