Answer by Aaron for how to count 16th note triplets

In the 1 and ah system, your best option is to subdivide. For example, a piece in 4/4 you would count as though it were 8/8.

X:0K:CM:4/4L:16"1"c2y"2"yy"3"c(3"4"c/2"&"c/2"a"c/2 "5"c"6"c "7"c`"8"c

However, there is an alternative system devised by Richard Hoffman that covers sixteenth-note triplets quite well. His mnemonic for a full sextuplet is Ta va ki di da ma. You would extract the appropriate three syllables depending on where in the beat the triplet falls. So, for example:

X: 1L: 1/16K: CM: none(6"ta"c"va"c"ki"c"di"c"da"c"ma"c | (3"ta"c"va"c"ki"c "di"c2 | "ta"c2 (3"di"c"da"c"ma"c

Richard Hoffman. 2009. The Rhythm Book 2nd ed. Franklin, TN: Harpeth River Publishing.
http://www.takadimi.net/

The Takadimi system is nicely explained on Wikipedia.