the first thing to do is grab a piece of dark green fimo a extend it with something smooth like a glass, then with a knife cut small pieces looking like leaves

next step is to do little thin rolls and molde it the eay you want as you can see i made this woth different sizes and then connected them, after that you start to put the little leaves you made on the first step connect them on the place you want very smoothly so won't leave many marks of the connection with the black fimo

don't forget to make 2 little holes one of each end of the necklace so then you can put the rings to connect them to the string , put in the oven for about 30 minutes with the temperature of 110Cº, when it's done put some varnish on the top and voilá you have a beautifull piece for a necklace :)