Saint Lucia is a small country of course, but there is quite a lot to see packed into the 200 plus square miles on the island.  Tourism is largely contained to the western coast of the island, and it's likely that especially any first-time visitor would find themselves somewhere along the western (Caribbean) coast.

This leads to a basic truth, which is that there is a northern and southern half to the island.  The northern part is more populated, more touristy, and flatter.  It also contains the capital of Castries, which is a popular destination for duty free shopping and a busy port for cruise ships.  The southern half is rural, mountainous (containing the famous Pitons), and better for activities like scuba diving and snorkelling.

 Most people likely care about how much money they are going to spend, and Saint Lucia isn't exactly the cheapest destination a person could choose.  Renting a car is very expensive, but so are taxis.  The positive about taxis is that the rates are set in stone so that the drivers cannot try to manipulate their prices to rip you off, but the rates are still probably more than most Americans (or British) would find to be acceptable.  Therefore, getting around isn't going to be a cheap proposition.  The pity about this though, is that minimizing these costs while a person stays at a resort will rob them of the ability to see the other parts of the island.  With so much to see there, it's probably better to save up more money before going to be able to move around than to go there with the mindset of not spending any money on it.

With the assumption that those who are going there are going to try to take in what the island has to offer, there are a few good tips to follow:

1)  At least once, try to take a water taxi, as this is an excellent way to see the island from another perspective.  Not only that, but it's just very relaxing to be on the sea with the wind in your hair.  The guides are usually very good about pointing out things on the way.
2)  If you're going out to eat, it's probably best to try to avoid chains such a s those found in Rodney Bay and venture out a bit if you're really wanting to sample the traditional fare of Carribbean food.  The Hummingbird and Dasheene in the Soufriere area are excellent choices.
3)  There is a 'drive-in volcano' and botanical gardens south of Soufriere that are worth going to.
4)  The best duty free shopping is in Castries at Pointe Seraphine.  There's also duty free shopping across the harbor from Seraphine but it isn't as recommended.
5)  If you can book an activity in the rain forests at some point, it's very recommended.
6)  Of course, see the Pitons while you're there.  This is the national symbol of the country....and for good reason.