It is important to wash locs with a good moisturizing shampoo. Remember, the key to beautiful natural hair is moisture, moisture, moisture! My current favorite shampoo is Carol's Daughter Black Vanilla Herbal Shampoo for dry to very dry hair. I like the Black Vanilla shampoo because it moisturizes very well without the use of a conditioner. Look for shampoos containing natural oils (olive, coconut, safflower, sweet almond, etc.) and/or shea butter. If your locs are fully matured, the use of conditioner is fine every 2-3 washes; it is not necessary to use every time you shampoo. Too much conditioning can lead to build up in locs.
Special Note for Baby/Teenage Locs:
If you are new to locking, you need to take special care not to agitate your baby locs too much. For the first few weeks you should clean your scalp with astringent (like Sea Breeze) or witch hazel (which is less drying). Saturate a portion of a clean washcloth and gently rub your scalp along the parts and between each loc. When you do start to use shampoo, you should avoid vigorous scrubbing for a few months. During the first 3 months of locking, I sectioned my baby locs into 4-5 sections and rubber banded the ends together to keep the locs from untwisting. Instead of using the shower head, use a container of water and gently poured that over the hair to wet and rinse the shampoo out. Take special care to just focus on washing the scalp for the first few months and not do too much vigorous washing of the baby locs themselves.
You also want to avoid any shampoo that espouses to help with "manageability" or "dangling". Locs NEED to tangle; that's what makes them locs. This seems very obvious, but I almost ruined my first set of locs using Organic Root Stimulator Uplifting Shampoo (an otherwise great shampoo) because I didn't think about the word "manageability", I just was focused on clarifying (see below). For someone with baby/teenage locs (I'd say up to one year) conditioner is not your friend. Conditioner will cause locs that are not fully matured to unravel.
Clarifying (and Dandruff Treatment):
It is important to avoid build up in your locs as much as possible. The best way to avoid buildup is to prevent build up. Shampoos, conditioners, styling products, dirt and lint can all accumulate and contribute to build up, making your locs dull and stiff. The best way to avoid build up is to avoid using too many products in the first place. However, every few weeks you should use a clarifying shampoo to remove any products that have built up in your locs. You don't want to use clarifying shampoo every time you shampoo, as they can be somewhat harsh and drying. You can use a clarifying shampoo such as Neutrogena or Panteen, or seek out a shampoo with more natural ingredients such as Avalon Organics Lemon Clarifying Shampoo.
Another way to clarify your locs is with the use of an apple cider vinegar rinse. There are many recipes for ACV rinses out there. Personally I simmer 1-2 sprigs of fresh rosemary in 2 cups of water for 15 minutes, then add 1/4 cup of apple cider vinegar, about 1/2 tablespoon of olive oil, 3-5 drops of tea tree oil, and 2-3 drops of either peppermint or lavender essential oil (depending on my mood). You can use this rinse either before shampooing by saturating your hair and scalp and allowing to sit for 15-20 minutes, or use it as a final rinse after you shampoo. The apple cider vinegar smell will dissipate as your hair dries. ACV is great for removing build up and helps treat itchy, flaky scalp by balancing the pH of the scalp. Rosemary is good for people with dark hair (i.e. most of us) to help bring out the natural highlights, and also helps treat thinning hair. For additional clarifying, you can add the juice of 1/2 lemon to the rinse. Lemon juice also helps break down oil and product build up.
Products to Avoid:
It is important to read the labels of hair products just like you would with food, and like food, products with natural ingredients are better for you than artificial. My general rule of thumb is that if I can't pronounce, I don't want to put it on or in my body. Not everything I use is "all natural" and I don't think you should feel pressured to use all natural products just because you have natural hair. It's just a rule of thumb to stick with as much as you can. However, here are a few products you should look out for and try to avoid when you look for a good shampoo, particularly if you have sensitive skin:
Sodium lauryl/laurth sulfate. This a very common detergent found in shampoos that causes soaps and shampoos to create lots of foam, but is also a skin irritant. It dries out skin and hair because it is an effective degreaser; however our skin and hair needs some level of oil to be healthy. We have been conditioned to believe that more foam means better cleaning, but this is not necessarily the case. Natural products will have less foam than shampoos containing this chemical, but work just as well.
Propylene Glycol. This is another common ingredient in shampoos and conditioners. It is a humectant, which are supposed to retain moisture in hair and skin by attracting water, however, they can also leave a suffocating film on skin and hair. Propylene glycol is also used in industrial products, and can cause skin irritation.
Silicone Oils (eg. Dimethicone, Cyclomethicone, Copolyol). These chemicals are classified as emollients, which are supposed to prevent dryness. They are often included in hair care products to produce shine for the "appearance" of healthy hair. However, these chemicals create a coating on the hair that blocks the absorption of substances that are actually moisturizing and nourishing to the hair and scalp.
You can find a more extensive list of common harmful chemicals in cosmetic products here.