Yeah, what John said
- I think all three of us were answering at the same time. How's that for service!
One other bit about dropping notes from a chord. The fifth and the root are usually actually the least important notes in the chord, and sometimes you just can't make a complete chord on a ukulele (especially for chords that require five different notes).
Some basic rules...
1) The fifth ('A' in the case of a D chord) can almost always be dropped with no harm, no foul. The exceptions are if it is diminished (A-flat) or augmented (A-sharp) but both are very rare in popular music.
2) As counterintuitive as it may be, the root ('D' in the case of a D chord) is rarely essential it would be the second choice to drop.
3) The third is pretty important in establishing mood and movement. It should rarely be dropped, except in the cases where it is "suspended" to a fourth or dropped in favor of the second (sus4 and "2" chords, respectively). Or, in the case of rock, simply dropped (making a "power chord") to emphasize the rhythm.
4) The 7th is pretty important - quite possibly the most important note of chords that have a 7 - especially if it is a dominant 7th (flat 7).
5) The 6th is not as important as the 7th but it is often used in establishing a riff so you should be careful about dropping it.
6) The 9th, 11th, etc. all include a dominant 7th - and that dominant 7th is so powerful that the 9th, 11th etc. get pretty lost. I.e. if a D9 is called for play a D7 if you have to - don't drop that dominant 7th to make the 9th. If you do, you have a Dadd9 chord and it is nowhere near as close to the intended D9 as the D7 would have been.
7) Trumps all above - rules were meant to be broken. Play your uke and have fun.
John