Customizing the look of your bike is great but before we even get to that, make sure you have the proper safety equipment. If you have not yet gotten a quality helmet that meets all quality standards, do that first. What's the use of having a great looking ride if you're risking brain damage with even the tiniest mistake every time you hop on? Make the dome cover part of your look. Designs and colors are available, head transplants are not.
The optional safety items like leathers, gloves, pads, etc. might also be on your list of things to buy. If so, good for you, but they are considered more optional. Some of these products do add to the comfort of your ride. If you wear something less cover-all than a full face helmet, goggles or good sunglasses may be in order. A cozy riding jacket is also a smart idea, especially in colder weather.
The further you plan to go on your new bike, the more essential it is you have some way of carrying your stuff with you. This is especially true if you plan on road trip vacationing with your bike. Saddle bags, add-on storage compartments or a backpack of some sort at the least will be needed. I personally prefer storage compartments but many people prefer one of the non-permanent storage options.
Comfort is a major consideration when it comes to riding. Does the stock seat work for you? Many people find that this is not the case, especially for longer rides. If this is true for you, you might want try out a custom seat. If you always ride solo, you'll want one kind of custom. If you often have a passenger onboard, another may better fit the bill. You might also want to consider a sissy bar and extra pegs so your passenger is more comfortable as well.
When it comes to the pure looks department, there are so many items to choose from that the choice gets difficult. Are racing stripes or flames your thing? Maybe a custom airbrushed tank would look nice on your bike. You can also just shop for nice looking stick-on decals. They make some incredible designs and they're easy to work with. Maybe new custom pipes is the look you want. All of these options contribute to a great look.
If you do want to customize the look of your bike, don't rush the process. Especially if you don't have a rock solid plan about what you want to do, looking at the wide variety of options is advisable. Also, before automatically buying the cheapest accessory whether it's grips, chrome pipes or a custom seat, do some research. A custom look is great, but make sure you are getting quality parts.
As far as finding the right parts goes, my preference is to shop both online and at local stores. Get ideas and compare. Once you're pretty set on what you want, look online specifically for the best price from a high-rated seller with good customer support. Places like Amazon are great because there are plenty of customer reviews which tell the story.