Print at 66% from original files. You can get 2 triremes on one A4 card by printing non-centered and running the card in again bottom.first. Smaller is possible but that means a pentekonter will be a nightmare and troops become meaningless blobs.
Use clothes-pegs or some other small clamp to hold edges while gluing - especially prow and stern.
A pair of blunt-ended tweezers also recommended especially for after ship is on base if anything needs adjusting. Make it complete before sticking to base.
Rest of tips are scribbled on a trireme print below.
Glue the ships to the base along the hull lower edges. A bit of thick paint can give a hint of a wave and add
some adhesion when dry.
Oar sections can be horizontal as if out of water or edge glued to base with again 'paint foam' to help hide edges and glue them down.
Add a little oar-wake and lhull-wake on the painted base. The base should be 2-3mm thick.
Write ship name at rear of base in white marker so it looks like foam from a distance.