Can be done several ways depending on where you are. Outside APW u can use your 30 sec stun to split 2 or 3 mobs, u can leash, u can FD several times and hope that one stays behind, u can use secret of ice to snare one of a multipull then FD and get back up to tag it..
In APW its harder since mobs hit very hard...the methods i usually use is make sure we have mezzers in the raid lol or try the multiplepull method and hope one finally stays behind, or u can use a second FD puller, pref a monk, which makes pulling in APW a walk in the park. In some cases when u dont have a second monk u can use an INVUL tank to suicide while u tag one to raid (least preferable way). But rule no.1 is learning what mobs can be mezzed and which cannot Well these are my experiences.....others may do things differently. Hope this helps. 

You can also use Rogues to tag and take  one to the raid then escape then you fd.I have found doors work really well to split mobs up too.Also on a few mobs you can pop RITW/find the center or magnificant drunken stagger then with Secret of ice up hit one(make sure its not immune to the snare) super jump away to create seperation fd,popup  then tag the snared one.
I would say as a monk experiment a little and you will find ways(and yes fast ways)

Yeah several ways to split in apw as solo monk. I never really gave the snaretactic much time as i found most mobs unsnareable in apw. Of course if you learn which mobs can be snared then thats a really good way to split. The doorbug is also a good way but can only be used in certain spots. Until they give us a random mob reset the far best way is to split using 2 monks when the mobs are unmezzable.

When u get a working raiddiscipline there will be no need to mark mobs prior to pull to know which ones to mez on inc. Will speed things up when u get that into the routine:)

another point u may want to look at is as ur grp does encounter mobs and when u use other class to aggro pull  n split mobs watch carefully the mobs them selves i noticed  time or two that a mob's will be pulled and when the puller runs out aggro range the mob will turn to reset

i know for sure in apw  to vicus in that room before to go thru that archway to vicus room there two female mobs there on each side of the archway together there hard on a raid so there split tanked and both outa  each other aoe range .

 so tank went to the right and we all was in the corner facing the mobs both tanks tagged each mob same time  but tank that was with us in corner died but i noticed  that it had turned and started to reset before it was tagged again.

so there diff formulas u can use on that situation so definitly watch mobn behaviors n pathing