Sorry in advance, I know this is going to sound overly negative. But I didn't like the island much at all.

Most US airlines fly into UVF which is on the east coast of the southern end of the island. Unfortunately the vast majority of the resorts are on the west coast of the northern end of the island (great planning guys). So you'll get treated to a 45 minute shuttle bus trip on windy 2-lane roads where the locals drive like complete maniacs (think NYC cab drivers in the jungle).

Make sure you pick a good resort (specifically one with a variety of food options) because chances are you won't be leaving it. We stayed at the Sandals Halcyon Bay (a very meh experience). Right outside the entrance was a highway that was virtually un-crossable, not that there was much to walk to anyway. Uber/Lyft was not a thing when I was there, so maybe getting around has improved since then.

Another thing to note is that there are no private beaches in St Lucia, even at the resorts. So while you're on the beach trying to relax the natives are walking by and trying to scam you and/or sell you things. This got old really fast so we never returned to the beach after the first day, total BS.

There are a lot of good excursions and side trips you can take. We took an air/land/sea tour of the Grenadines that was the highlight of our trip (link below). The rainforest tours are also interesting. Skip the "volcano" tours. The cone is collapsed and its basically just a smoking sulfur pit.