I use a sterile syringe with the sharp needle attached. I keep a box of sharps to vaccinate the puppies, but if you don't have one, you can ask your doctor or vet for one rather than buy a whole box. (Unless you plan on making these on a regular basis. In which case I may just show up at your door.) If you do an internet search for Grand Marnier chocolate covered strawberries, you will not find them made using the sharp needle. They tell you to use a pastry injector or a syringe without the needle, which I'm sure work fine too. I've never tried them that way. Doing it my way you can inject the liquor into the stem-top rather than through the red berry part and it helps keep it from oozing out.
The size of your berry will determine how much Grand Marnier you will draw up into your syringe. There are 5 cc's in a teaspoon. Start by drawing up 5 cc's and inject the needle into the top of the berry, right next to the stem at the top. Go slowly. The slower you go, the more you can get the berry to accept. When it starts bubbling at the top, you are probably done. Put the berry down and finish the rest. You are just going to have to taste one to know if you have enough Grand Marnier. It's a dirty job, but somebody's got to do it.
Now for the chocolate part. I am partial to dark chocolate, but you can surely use your favorite. Basically, you want to get the very best chocolate you can like a Valrhona or Callebaut but you can use chocolate chips too. Melt the chopped up chocolate slowly in a double boiler with a scant teaspoon of vegetable shortening added in. You can add a tiny drop of heavy cream if you like, if you are using good chocolate but it is not necessary. Don't use the microwave. The chocolate can seize up. You want your strawberries to be dry as well. Any moisture will cause the chocolate to seize up and get dry and grainy. When the chocolate is nice and smooth, grab the berries by the leaves and dip into the warm chocolate. Let them dry on a wax paper covered tray. You can put them into the refrigerator to set. I leave them in the fridge because I like them cold, but you can leave them out for your guests unless it is too hot or humid in the room.