it's all very relative - depending upon your current skill level & how much you wish to challenge yourself.
once you've got a good understanding of the 'fundamentals' of sleights or flourishing, then choose 3 or 4 effects to focus on at a time - make sure each is something that you both enjoy/want to do & something that challenges you - get the all moves wired and most importantly - make the effect 'your own' before moving on, then once you've moved on - continue to practice them regularly..
the magic is not in the mechanics of an effect (easy or difficult) - the magic is in you - even the most basic books & dvds can yield incredible effects when given the right performance.. and everything is difficult to truly "master"..