The most important thing for newcomers to learn is you have to haggle. Retail music equipment is a very competitive market. Most stores will match or beat other stores prices. It pays off to call around locally and nationally, visit different stores and search online for good deals. Go into any retail music store and the majority of equipment you will see is for beginners. Do you know why? Because this is where they make most of their profit. Beginner musicians are also beginner shoppers. They stand to make more money off the less experienced shoppers who don’t know how to bargain.
List price is a fantasy in the music world. On most items you should expect to pay 25 – 50% off the list price. Guitars and basses usually 25 - 30%. Some accessories 50%+. For instance, electric bass strings are marked at $45 list, but can be had for $14 and they’re still making a profit! Stores will be more than happy to sell them to an unsuspecting beginner at $45. You might even think you’re getting a good deal when they advertise them at 2 for 1, but you’d still be paying $45 instead of $28.
Shop around to get good deals. You can’t just go in and say, "Give me that for 50% off." You have to hunt. And, you’ll get better at it as you do it more. Ask more experienced musicians if you’re getting a good deal. The salespeople will always tell you that you are.
I recommend developing a relationship with a nice salesman that’s been around for a while. This is hard at many stores because of the high employee turnover. Most employees get a job at a retail music store so they can get the coveted employee discount. (To get stuff for the band, man.) Find out with whom you’re dealing, ask how long they’ve been working there and in the industry. The people who have been there for a while will stick around longer and will be more knowledgeable. By dealing with the same person, you will have an easier time and will be less prone to getting ripped off. They will realize that you’ll come back to them and they’ll treat you right as a result. They will remember what you’ve already purchased and will know what goes well with what you have. It will also make returns and exchanges easier.
Beware of pawnshops! I would only recommend these to experienced musicians who know what they’re buying. Many of these very used items are marked at the list price for a new item. You might be able to get the same thing new for less and you’ll have a warranty.
Buying online can be tricky too. Some things, such as guitars and basses, can sound radically different from one another. I would be weary of buying something I haven't played. Things like accessories shouldn't be a problem. If you do buy online, check the return policy before you check out! Some places don't take returns at all! I found out the hard way.
Knowing all this should save you quite a bit of dough and headaches throughout your musical career. Good luck with your shopping.