How do I safely place an extension ladder on an uneven surface?
It may be easier to find one place where you can safely place the ladder so that you can get onto the roof.  Once you are there you can remove the leaves.  Of course this depends on the how steep the roof is and your comfort level of being on the roof vs being on a ladder.  

Unless you plan to buy a leaf blower anyway, make sure there are only dry leaves in the gutters.  If they're full of decomposing leaves, you'll have to scoop out the gunk and a leaf blower isn't going to cut it.