I usually use a riffle shuffle with sleeved cards with not problems. What I do is have the top of the sleeves pointed away from me, split the deck into two parts, and riffle them so they are in a V shape with only the bottom right corner of the left pile over lapping the bottom left of the right pile.
If you sill cannot shuffle them that way the next best way is a mash shuffle or side shuffle. For this one take the deck and split it in two piles again, then take the two piles and 'mash' them together along the long side.
There are other ways of shuffling as shown on Wikipedia, but from what I've heard these are the two techniques that create a random deck the fastest.