Mandolins and ukuleles both usually have standard tunings. Like any string instrument, it is possible to use a variety of tunings. Retuning the ukulele to a mandolin tuning makes it possible to duplicate mandolin chord voicings and mandolin licks on the ukulele. However, in addition to the tuning, you can also perform mandolin strumming patterns and rhythmic techniques on the ukulele.
Tune your ukulele to standard mandolin tuning. Standard tuning for the ukulele is G-C-E-A which is a C6 or A minor chord. Standard tuning for the mandolin is G-D-A-E which is the same as the tuning used for a violin or fiddle. The G string on the ukulele is a thin-gauge string. The C string is the lowest and thickest string on the ukulele. One option for tuning the ukulele like a mandolin is to simply keep the high G string tuned to high G. The second option to replace the G string with a thicker gauge string. This also involves filing the slot in the nut so that the string fits.
Learn mandolin chords. The altered tuning changes the relationship between the notes and strings. This makes it necessary to learn mandolin chord positions on the ukulele. (See Resources for mandolin chord charts)
Play the chords with a mandolin pick. Mandolin players typically play with a medium-sized, tear-shaped pick. The pick is either medium gauge or heavy gauge. The small thick pick helps mandolin players play at blistering speeds.
Learn the major minor scales in the new mandolin tuning (See Resources for mandolin scale charts). Practice the scales with alternating up and down strokes with the pick. Practice the scales with a metronome. Play the scales as eighth notes, triplets and 16th notes.
Listen to a variety of mandolin players such as Homer and Jethro, David Grisman and Sam Bush to gather ideas and develop technical chops.