Dig -> Earthquake
Draco Meteor -> Dragon Claw
Feint Attack -> physical coverage move
Hyper Beam -> physical coverage move
Soft Sand -> ???
Lacking info on Nature, IVs, and EVs. Ideally, they'd be a bulky set with leftover points going into physical attack.
There are really only 2 "problems" with Flygon as a Pokemon. It's probably the weakest psuedo-legendary in terms of raw stats with no Mega Evolution to fix it, and it's movepool is very limited for covering it's weaknesses. 4x weak to Ice is especially painful, and is a common type for either coverage or filler moves. Biggest stumbling block is going to be Fairy, for which the only options in movepool are Iron Tail (70% accuracy) and Steel Wing (90% accuracy).
Examples of builds can be found here.