If you don't know an opening knights before bishops is a good policy. Or better yet you could seize the center with d4 maximizing your piece mobility and central control.
As black I'd try this:
An example of borrowing other ideas from other variations:
They usually move the bishop before the knight to keep f4 as an option.
If you play something like 1.e4 d6 2.Bc4 e5 3.f4 then capturing on f4 is probably the best thing to do because your dark-spuared bishop will make the position passive otherwise. After the capture on f4 you would be in some kind of king's gambit/Vienna position.
If you don't want to get into that then you could play ...c6 or ...g6 and continue developing.
I see this move quite often and I can't seem to find any theory on it.
If play goes 1. e4 d6 2. Bc4 Nf6 3. d3 - that resembles Vienna opening where I have made quite passive move - d6.
3. Qe2 and Nc3 are other possibilities.
I am particularly uncomfortable with my darksquare bishop, because It feels like white can lauch a quick kingside attack and therefore I don't want to weaken my kingside with g6.
How do you approach this?