Primers are usually made with wax, collagen, silicone, or other products that will help in holding your makeup to your skin. For this reason, people tend to think using a base coat is only for people of older age or with facial scaring. Though true, I believe base coats are for anyone wearing makeup in general.
The type of base coat you will love and that will work best for you, will depend on what you want to achieve in your makeup application. If you know me personally, you know I wear a lot of eye makeup, so to me eye primer is an everyday thing. If you are someone who wants to attract attention to your smile you might get more out of a good lip primer than your usual lip liner and lipstick combo. Of course, the same thing goes for someone looking to even out their complexion with foundation primer.
I personally use three different primers. I have two different primers for my foundation and I have a separate primer for my shadow.
The first one I use is LuminessAir Primer.($40 HSN.com) Which is meant for my airbrush foundation and doubles as a moisturizer. This one goes on so smooth you can't really feel it on your skin. When used it can help keep my makeup on for 24 hrs or more. (if I weren't gonna wash my face.) The added moisturizer makes my skin even softer and more smooth, perfect for airbrushing.
~If you are going to use primer under a dramatic shadow look, I would also recommend using NYX Jumbo Eyeshadow Pencil in Milk instead. ($4 Ulta) If you use your finger to lightly apply the white color from your eye lid to your brow bone, you can use this as a primer and brow highlight in one step. Simply apply your shadow as you normally would or just apply a simple color along your crease and you will have a beautiful longer lasting look.
~If you are looking for another similar item to this one, I would also suggest trying L'Oreal Studio Secrets Primer. ($9, drugstore) I received a sample in the mail and I was impressed by the results. It has a very creamy texture but surprisingly goes on completely smooth. I have heard of people using this primer for face, lips, and eyes.
There are a lot of really good eye primers out there. My favorite would have to be Ulta's Base Coat. ($7 Ulta) It might seem like a cheap choice but I just love it. It is a cream base but it is so light weight that it glides right on. A lot of the primers I have tried cause my shadow to clump up in the crease, which is also why I do not recommend using an all over primer.
I personally prefer to use lip staining products that I can wipe off and still hold a little color. I have a hard time keeping lipstick off my teeth and chin so I gave up wearing it regularly. That is not to say that I don't have a preference on lip primers, it's just I don't bother purchasing it myself. There are times when I get dressed up and will wear lipstick out. When I do, I use any colorless lip balm under my lipstick. Most lip balms are made with wax so if you put a thin layer under your lipstick it should hold the color to your lips better. This will also help prevent the lipstick from settling into any cracks in your lips, that can cause your lips to look chapped.
I hope that helps answer some questions about how and when to use your primers.
Please feel free to leave comments and opinions on your favorite products.