Hi Richard
Unless you are staying on one of the 'Out Islands', you should definitely go out on a charter boat. Shore fishing on the main holiday islands (Mahe, La Digue and Praslin) is quite hard work, although especially on an incoming tide in the morning, where sand meets rock and weed, there is still plenty of fun to be had. On Praslin, there are some bonefish flats, and the fish are big (6-8lbs ave), but very few and far between. On a boat, expect to catch loads of excellent pelagic species, but don't hestitate to ask if the skipper can get you onto a spot where the trevallies hang out, so that you can chum them up and fish with light-ish tackle.
I say light-ish, but the giant trevally gets up to over a 100lbs! Others, like blue trevally and golden trevally are much smaller, but fantastic sport on spinning gear. I think they are about the best pound-for-pound fighting fish anywhere.
If you can get to one of the out islands, like Desroches or Alphonse, you may still have to get on a boat, but you can wander off for a walk and still catch great fish.
By the way, the Seychelles are just as gorgeous as people say they are and the photographs you see in brochures are true to nature. Be careful though, the Government keeps changing its collective mind about use of foreign currency. Check in advance if you can use american dollars in shops, restaurants and so on. Otherwise you'll need to buy lots (and lots) of Seychelles rupees. Also, don't be shocked by the prices! They have a deliberate policy to over-price, so that visitor numbers will be low (and less damaging to the environment), but profitable to the economy.
Strangely, a friend of mine says that the result has been a huge increase in the number of rich Russian visitors.
Anyway, let me know if you have more questions.
Cheers
Jason