I don't recall ever seeing to much instruction on scales and chords for drop D tuning. You will find drop D instuctions on tab and sheet music.
I would suggest 1st drop the D and noodle a bit.
Drop D is most usefull playing in the key of D or Dm. I also will use drop D playing in key G too. Find a few songs that predominantly use a D chord and noodle.
For every chord when playing the 6th string (which you've dropped) the lowest note is gonna be fretted 2 up from where you would with out the drop tuning. With a D, string 6 is open. With an E, string 6 is playing on 2 fret. F, 6th string 3rd fret. F# 6th string 4th fret and so on. D with an inverted F# bass is not hard to grab. Power chords turn into baring over 3 frets.
Drop D opens up some low end and gives the guitar another set of possibilites while creating another set of limitations. Playing in the key of A I would not drop to a D cuase that open E is to valueble.
You can play in any key with a drop D, add a capo and get a hole other set of tones to work with.
For drop G and other open tunings I'm sure a google search for 'open tunings' will yield some fruitful findings. Open tunings are common for slide guitar playing and again create some advantages and challenges.
Typical Banjo tuning is open to D or G.
