All the dings I've had are on the rail mostly near the nose.
The trick to shaping the ding to fit the rail is to put glad wrap, cling film, or whatever you call it where you live, over the resin.
First of all get yourself a ding repair kit which should include the following:
block of foam (only needed when foam dinged too)
Catalyst (to harden the resin)
A mixing tub
Some popsicle/icy pole/ice lolly, sticks
A tub of microballs, I don't know what this is and I can't be bothered getting out my kit to look at it, but it's a very light white dust which helps give the resin a white colour and makes it stronger when it hardens.
First make sure that the ding has dried out, leave it overnight to make sure. Put your mouth over it tightly and suck to see if any sea water comes out.
Sandpaper out the edges with rough sandpaper and cut away any remaining loose glass and sandpaper that back too.
Mix microballs with the resin in a little container. Only enough to fill over the ding and a little spare.
Now cut out a piece of fibreglass cloth to fit over the ding make sure it is slightly bigger than the ding itself. Once you have done this place it somewhere close at hand, as you will need it quickly later on.
If foam is missing from the ding then cut some from the foam block that should have come with your repair kit and make sure when it fits the ding that it leaves enough space for a glass job over it.
Now take some tape and create a barrier with the tape around the ding to make a little wall so that resin won't drip all over your board. A side view of the barriers should look like an L standing up. WIth the sticky side folded over onto itself to form a stickyless wall. The wall should be on the side of the ding.
Go back to the container with the resin and drop about 3 drops of catalyst in it. Be careful not to get this in your eyes as it will make you permanently blind!
Stir the catalyst into the resin and now work quickly as the resin will begin to set. Use the popsicle sticks to stir.
Apply a very thin film of resin to the ding.
Now place the fibreglass cloth over the ding.
Apply more resin to the top of that spreading it out and make sure to try to get the air bubbles out.
Once you think the resin is slightly more solid than liquid quickly remove the tape. Now get a sheet of cling film and pull it tighly over the ding. This should make the ding fit in with the rest of the shape of the rail. ALso you can now massage the resin to fit the form and push out airbubbles without getting sticky.
Pull the cling film down tight and tape it down if you feel this helps.
Now just wait about an hour, or two depending on how much catalyst you used. You can rip the cling film off earlier than that however you don't need to as the catalyst creates an endothermic reaction so it doesn't require air to harden.
Once the repair has hardened use the rough sandpaper to smooth down the ding until it's flush. Then use the smooth sandpaper to make it look good. You can apply another coat of resin on top of that if your board has a gloss finish, don't use microballs this time.
Although this process works brilliantly I have yet to make the board look perfect as I can never get the colour right. Microballs can help make the ding whiter. However my board has now begun to yellow so the dings are cleaner looking than the board.
Buy Solarrez or Suncure and paper back the ding. Apply suncure with popsicle stick. Put cling film over the ding. Put in the sun. Sandpaper as above.
It won't look as clean as above process.
THEN GO SURF.
TO make sure it worked suck on the ding after your first surf to make sure that there are no tiny holes on the edges or airbubbles that have created a hole in the resin. If you feel salt water on your tounge then fix that ding again.