Although the mill file (above) seems to be outsized for Z-Scale, it is incredibly helpful for knocking down raw edges and excess flash. It can also be used to true up a long edge, keeping in mind that a light touch is required. If you leave file marks, sandpaper can be used to clean this up.
The buildings are put together with glue, and this matter is subject to some personal taste. You will need to use a styrene cement for the assembly process, but there are several to choose from. The cements fall into two major categories: tube and liquid. The tube cement is the classic model airplane cement which has the consistency of honey and is colorless. It contains plastic solvents and liquid plastic. When using tube cement, apply small amounts of the adhesive to one or both surfaces to be joined, and then join the pieces together. The liquid type of cement is not cement at all, but actually a plastic solvent. If using the liquid, join the pieces together first, and then apply it along the joint line, taking care to keep your fingers away from the joint. The liquid solvent flows by capillary action into the joint, and, if your finger is on the joint, into the area between your finger and the adjacent plastic as well, leaving a fingerprint. Don't despair, however, for if you wait until the fingerprint has dried, you may be able to take the back edge of the modeling knife and scrape the print away. Sandpaper could also be used to repair the damage.
Liquid cements dry faster, but they do not fill gaps. Tube cements fill gaps, but need more care in management (meaning, the stuff may drool all over the place). Placing gluing tips over the tube openings will help regulate the flow of the glue. There are also tube glues with needlepoint applicators or you can apply the glue with a toothpick. Tube glues do have one definite advantage. When working on those tiny window shutters that so many of the kits seem to include, tube glues make the application of these things much easier. Just put a tiny drop where you want the shutter to be located, then take your trusty tweezers, pick up one of the little jewels and position it precisely.
One of the drawbacks to using plastic as a material for making building kits is that it looks like, well, plastic. Light reflecting off the plastic surface gives it that unique sheen. There are, however, a couple of ways to deal with this. One is to paint the structure with model paints. You can individualize your buildings in this way, but it does take more time to complete the structure, and may not improve its appearance. Being lazy, I use other methods to solve this problem. Some of the structures are made of plastic that represents brick masonry, and even have the mortar lines cast into the walls. I take liquid white shoe polish, wipe it on the brick areas, let it set for a minute, then wipe it off with a rag or paper towel. The shoe polish fills the mortar lines, and the rag wipes off the excess, exposing the brick faces. Several wipes may be necessary. The same effect can be made by using certain model paints; test on a small section first. This really sets off the brickwork.
In all cases, I assemble the structure, but I do not install the clear window material. Taking care not to glue everything (notably the roof), I spray the almost completed structure with a dulling lacquer spray. This process retains the original colors of the structure while dulling the plastic sheen. After everything is dry, I (almost always) go back in and install the window glass. Sometimes there are windows which cannot be reached, even with tweezers, so when using this procedure, it helps to plan ahead.
The Kibri half-timbered structures use self-adhesive, lithographed sheets of special paper to represent much of the half-timbering. Fortunately, the paper sheets are die-cut, which means that you simply have to peel them off their backing and position them properly on the walls of the building. This is best done after installing the window frames, but before joining the walls together, spraying the flat overcoat, and installing the window glass. If you examine the individual walls, you will note that the edge of the half-timbered area has timbers cast into the plastic wall. The balance of the area to be half-timbered is flat, smooth plastic where the paper is to be placed. Find the proper paper piece (which may be a task in itself), and peel it off the backing. Grasping the peeled paper with your tweezers, locate a long reference edge on the plastic wall, and match it to the same edge on the paper. (A second pair of tweezers is quite helpful here.) Apply this edge first, double check to see if the piece is the correct one and is properly aligned, then gently roll it out like a carpet, removing any window openings that are still filled by the die-cut paper. The rolling action helps avoid trapping air bubbles under the surface. Should you create an air pocket, open a small hole in the bubble with a straight pin, and gently squeeze out the air. Once the paper section is positioned, it is there for good. This prevents the paper from coming loose later, but does not allow a second chance. Because this process does produce some very handsome structures, it is well worth the effort.
Finally, if you want to work on your layout while you are working on the structures, you may find it helpful to take the bottoms of the structure kits and place them on the layout to give yourself points of reference. It is probably a good idea to mark the bottom lightly with a pencil so that you will know which bottoms go with which kits. As an alternative, you could trace the bottom on a piece of cardboard, cut it out, and use that as your layout reference point.