| If the plant is still in the container it came in - gently take it from the pot and check the roots. And the potting soil. Coleus are thirsty plants - and like to have a drink then be in damp but never water-logged soil. If the roots at the bottom are black and wet-looking - they've rotted and aren't helping the plant. If you find that there is a big mass of roots in the pot and they are starting to curl around in the shape of the pot, then you need to transplant - either into the garden or into a bigger pot if you plan to keep it over winter. If there is hardly any free soil left in the pot, or it is dusty-looking, then you definitely need to repot. Ask someone you know who has good houseplants, and pots their own, to show you how to root-prune and pinch back the top growth to keep a balance. If you know how - phew! If you don't, it helps to see someone else do it first. Then pot into a container that's an inch bigger all round than the present one, using some fresh mix. Don't push the mix down hard with your fingers because it flattens the air spaces and plant roots need air as well as water. Water after you've potted. Please remember that just because it's in a bigger container, or out in the garden, it is going to take weeks before those roots start growing into the fresh soil so you will have to maintain your regular watering. (If you moved it on into a much bigger pot when you bought it - it might easily be staying too wet because there are no roots in the big mass of new soil. Shift it to new mix in a smaller pot.) If you have got a bug infestation then a spray such as Confidor could help. Keep the Coleus plant away from your other plants so they don't catch the bugs, too. IME - rhizo always gives excellent advice so it's well worth following up on his suggestions.
Good luck! | 
