So obviously their are many more then just the four clairs such as, empathy, mediums, and the list goes on. I my self, happen to be a medium and I also have claircognizance, so lets take a look at each one.
Clairvoyance means "clear seeing". People with this ability have the gift of being able to gain information about people, places, things, and facts through the minds eye. Since this gift is obviously used with out seeing anything with our physical eyes, and it is used by seeing with our mind's eye, the third eye is the chakra used the most by these individuals. There abilities usually include but not limited to:
~Identifying psyichal symbols and mental symbols.
(this clair is a good problem solver and if you have this ability, meditation would be the best way to go to develop it.)
Claircognizance means "clear knowing". It is the ability to just "know" things about people, things, places, and such. People with this gift also manifests random thoughts and ideas put directly in your head. The claircognizance is identified with the crown chakra. To help develop this ability if you have it, a good way to guy is type or write, by writing the question at the top of the page, and then just writing the rest with out thinking. You can also pick up telepathy better.
The next clair we have is Clairsentience which is "Clear Feeling"
It is more closely associated with the "Gut feeling" or "Heart feeling". People with this ability usually can get premonitions from touching things, people, and places. They can even somtimes get a sense of history. The premonitions are not visions though, they are gut feelings usually. The Heart chakra governs this clair, and the best exercises are more like just using your ability.
(mind you im not an expert at this clair)
The last clair is Clairaudience for "clear hearing". This ability is mostly associated with the chakra that sit above the brows near the ears, the are not mentioned in the 7 chakras but we have way more then 7. The people get information usually through a voice in their head, from a divine being or guide. The energetic sensors pick i up, and unfortunately this ability also does not work on demand, it work when who ever decides to talk to us, just these people get talked to more often to help their problems.
Some good topics I would like to cover is that if you have a clair ability or even more then one, please remember two things, The first being that we do not know everything, and never claim to know everything. Secondly you must know that using your ability for money, or anything else is miss using them and ultimately will lead to you loosing them. Also if you dont practice with them you won't loose them, they will just go dormant, to preserve your ability. Lastly, anyone can develop psychic abilities just some people have more of talent for it, kinda like some people are more inclined to sports, art, music, etc. psy is and such is just another area of expertise, some are good with divination, some are good with talking with the dead, some are good with all form of divination. The only real way to know is practice.
Kudos to LivingForest for coming up with all these details.