As aiwas (aka petrucci expert) said he likes chromatic stuff off course as much as possible with alternate picking, slides off course but also 3-note per string scales and licks. Since Steve Morse uses this type of technique when speeding a lot and Steve is one of John´s most inspirational players, Petrucci uses it often as well.

Tapping was somthng that John used to do back in 80-s (check out Fortune In Lies and Ytse Jam for example) but don´t use it that much nowdays.

Sweeping of course and he likes those wierd 4-string sweeps like that one in Under A Glass moon solo wich he combine with tapping and those sweeps in Beyond This Life solo.

He´s not a big string skipper but than again check out Erotomania last solo. Wah-wah is somthing that John adores especially on Awake album.

And this lick is also one of John´s fav. licks

e|-14-15-14|-12---------|
B|-------------|-----15--12-|

Lots of variations on this one. lternate pick.