One of the things I find most difficult in my ukulele learning process is to keep time while playing. An excellent exercise is to play with others.
My friend Ganymede Gwilym and I often like to play a series of chords to practise keeping time when playing together. Today we had great fun doing a video of an improvisation on 4 chords of Clocks by Coldplay (initially D Am C Em, transposed to G Dm F Am). Trying to keep a steady ukulele fingerpicking while the guitar is changing rhythm is excellent practice.
Here is our rendition of passing time :