Determine what the primary use of the ear protection will be. Hearing precautions should be taken by more than just musicians. Some companies, like Hearos, design their products tailored to specific activities, such as using firearms, using power tools, going to car races and many others, including music. For example, Hearos makes specially designed musicians' earplugs.
Experiment with different forms of ear protection. There are in-ear varieties as well as over-the-head earmuff-like options. Whichever is most comfortable for you will be the option to explore. If you have an aversion to putting objects in your ears or abnormally shaped ear canals, the earmuffs will likely be more appropriate, though a bit more bulky.
Explore options within your chosen variety. In-ear protection has a wide range of variability. You may prefer specific musicians' earplugs, which cut out certain damaging frequencies and let others through, or you may prefer simple foam earplugs which lower all frequencies in the decibel level that reaches your eardrums. There is not as much variation with the earmuff type of ear protection, but you will want to find a specific product that fits very snugly on your head, completely covering your ears. The tighter the muffs are over your ears, the more noise isolation you will receive.
Check the noise reduction rating of all products you consider. The noise reduction rating, often abbreviated "NRR" on packaging, measures the number of decibels reduced by use of the product. A higher number is better.