1. Stay away from Woodland Scenics Realistic Water. It's gunk.
2. My favorite is Envirotex Lite...a resin based water type.
3. Make sure you mix it well at the right ratio.
4. You can tint it with ink, but make sure you don't overdo it.
5. If you want to add grass/weeds/reeds, add them when the resin is almost set. Otherwise it will creep up the foliage and it looks silly.
6. You can sprinkle leaves and turf on top. If you do it when the resin is wet, it will sink to the bottom (which is cool). If you do this when the resin has almost set, it will stay on top.
7. Make sure the terrain piece is on a flat surface so you won't get a skewed water level.
8. Try to pour if the air is not too moist...otherwise the resin may get a strange film on top.
9. Try to pour in thin layers. If you want a deep area, build up the layers...one per two days.