The most common flourish I've seen starts to involve through-the-fingers work, so I would recommend first learning some elementary baton twirling moves with a devilstick (or even a baton!), to get the feel.
Anyway, whether or not you are prepared in these respects, the (for want of a better name) common flourish goes like this:
This move is basically the beginnings of through-the-fingers twirling, and you can add another half-spin per finger used, and maybe even go back though the fingers the other way (I wimp out of describing all this in detail!)
There are lots of other flourishes, but I don't know many of them! What I do do is flourish-like throws in which the club is spun in various ways (usually double spin) and caught in the same hand, in the style of a flourish. One I discovered recently is closely related to the above description, except that the initial pencil grip is used to flick the club into a _reverse_ double spin, and then caught in a club-passing style catch---the club does all its flourishing in mid air (and looks good if you can send it up parallel to one of the other clubs, which is doing a regular double spin)
Anyway, given a flourish, next is the question of where to fit it into patterns (passing patterns as well of course...). Site-swappers will probably just need to try changing even-numbered throws into flourishes (a 2 might be hectic, try a 4 first??)
I think I've just worked out that my usual flourish (3-club) pattern is a ...4440... siteswap, the second 4 being the flourished club (maybe it should be written ...4F4F..., where the F indicates the hand is doing part of a flourish?)
As for which tricks look good with flourishes, I would say that the average audience would consider it a trick in itself!
I have taught this to many people and found that the best way is to give a simple crude definition so they can get the movement and let them refine it with practice and lots of it!
Learning the flourish in the right hand:
Preliminaries:
1) learn to throw one double spin from left hand to left hand and and then back to a cascade. You should be able to isolate the right hand. Chen you can do this wave the right hand about wildly and widely.
2) learn to cath the club in Rh in a pen grip, with the club vertical body pointing down and knob pointing up. (palm down)
Twiddly Bit.
3) With 1 club in the RH in pen grip rotate the hand 180 degrees, till the palm is pointing up (club vertical body upward).
4) Let the club fall between the index and middle finger (club now vertical with body pointing down (palm up))
5) rotate the hand through -180 degrees (gripping club with middle and index finger) club vertical body pointing up -palm pointing down
6) let the club slip forward till the handle hits your palm and close you hand (thumb and fingers) around the club and you have finished, throw a single right to left cascade
so the movement is grip, rotate, drop, rotate, slip, grip
Its really important to be able to do this automatically, when i do it I know that as soon as i have caught the club in the pen grip my hand will do the rest so i can worry about the left hand self double (or single or triple ...)
Practice both hands otherwise like me you will become lopsided!
Something that hasn't been discussed here so far, I think is the danger of flourishing too vigorously and having the club slip out of your hand, fly across the room and hit an innocent juggler or bystander. Very embarrassing. Anybody else done this?
1) Continuous Flourishes - Once you can do the basic flourish, try starting a cascade except with doubles. This will give you just enough time to flourish your right and left hands alternately -- really nice looking trick.
2) Flourish Transfers - **HARD** Throw a double self with your right hand, flourish with your right, throw a double self with your left hand, transfer the flourish (continuing the motion) to your left, and continue the trick. Really pretty!
3) Flourishing while Passing - Can easily be done with right hand after throwing left to left double (either in 2-ct or 4-ct). Also possible to flourish with left hand but requires you to flourish quickly and do a shower throw to the right. The "loopy" a.k.a. shoulder pass is a nice trick to go into after flourishing.
Other notes: Don't just flourish in one plane. Experiment with horizontal and skew planes. Try bringing your right hand flourish over to your left side and flourishing thru your pattern. There's a lot of neat things to do. Be imaginative!
Left Handed Flourish
To get this when passing every others, you need to be able to catch the club thats coming in to you as a pass upside down. To do this you catch it with what I think is called a frog catch. Put your hand in the normal catching position and rotate it 180 degrees clockwise so that the palm of your hand is facing to the left. If your hand is in this position it is fairly straight forward flourishing the club thrown to you. (This is the same catch as for 3-count flourishes). To get the time for this:
pass out as normal
left hand self
right hand double to the right hand
catch the club coming in and flourish it
right hand pass
I think this is a really nice trick but I'm biased as I'm left
handed. If you want to be really flash, you can pass a triple out the pass before and that gives you the time to flourish both clubs (I'll let you work that one out for yourselves)
Double Flourish
Another nice one but this is for solo juggling (I have got it to work when passing but it's a bit quick). Go into columns. Throw the single club as a high triple or a quad, catch the two clubs and flourish them, catch the single on the way down.
Hope people like these.