For that "Wet" look...

Something you might want to consider trying, Delta Ceramcoat, available at your local craftstore. if you cant find that try "mod podge" the only problem with mod padge is that on hot days or in the sun, it can tend to get tacky. Both of them look horrible when you put them on but trust me they will dry clear

Try using Humbrol Glosscote. It looks nice and wet, good for mud or dewy grass.
I hear that Future works well for dewy grass as well.

Clear epoxy for small spots and Lilquitex, much the same but sold more economically, for larger areas.

You can use future for small puddles.

QUOTE: Originally posted by Anthony14 You can use future for small puddles.

Not if there's any depth to the puddle since Future looses much volume as it dries. You'd need dozens of layers to get any thing like a puddle. To gloss up a wet spot this is fine.
Whatever you uses, you'll want to paint the area that's wet a darker color that the surrounding area.

or clear resin would be fine too. but that's more for making the gradual depth of the puddle look , then u just gotta use a darker color for the surround "mud" and gloss coat them for that moist sheen