Yes, use a grout float to tamp them in but if you need to keep some of the joints in line the wickes straight edges (used for plastering) have a fine point/edge which works well....
make sure you use a suitably sized notched trowel, otherwise you'll waste time trying to clean out excess ady. Alot of tilers make the mistake of rushing mosaics especially the grouting and it looks a mess. If walls arent square you can open out the sheets so its less obvious.
Whatever make of mosaic i fix I try not to have any cuts. Use white adhesive with a long open time.