Just to clear up any confusion, a direct smear doesn't contain so much fecal material that you can't see the slide underneath. You want to get a small amount of the sample, mix it with a good amount of water so that you can see through it, and then put the cover slip on it.

Fecal floats won't find giardia unless they are just infested, so smears are good to do in most cases. I usually do a smear first while the float is taking its 8 minutes to do its thing. This is also a good time to break open any tapeworm packets to look at the eggs(if you want to).