How do I get a crisp clean slices after I cut a cake? Usually I don't get very sharp slices. I use mousse/SMBC/fudge fillings with/without fresh fruit pieces.. 

Have a jug of warm water and a clean cloth on hand - after every cut, dip your knife into the jug - then wipe dry - that way your knife will be clean for every slice.

Another good point to remember - make sure the knife you are using has a blade that is as long as the cake is tall - i have seen people cut a tall cake with a short knife and after one slice there is cake all over the handle - irkkk.

Bluehue