I've mentioned before that you need to include a bridge support at the end of every bridge section. I've shown you an example of long spans with inadequate supports. Well, here's one where the modeler actually did it right. This HO scale bridge has a long section made up of three spans crossing above another track. The modeler was careful to include a bridge trestle (vertical support) for every span end and designed them so as not to block trains passing on the track below them. The modeler has also included a cement foundation under each of the trestle bases as well as appropriate cross bracing between adjacent trestles. On the prototype, a bridge like this could have been built in the 19th century, but in later years would likely be a candidate for a redesign to use a single long span instead of these three short spans to eliminate the complex trestles over the lower track (which in turn would provide increased clearance for larger rolling stock on the lower track).
I saw an ad on television recently that touted the importance of a good foundation. Just like the prototype, your model structures could be quickly and easily improved with a good foundation too. Look around at the buildings in your neighborhood; the foundations are usually visible as a narrow strip of concrete below the wall that makes up the side of a building. Sometimes the foundation is painted in the same color as the rest of the wall, sometimes it's left bare. Whatever its color, a quick box of styrene strip material will easily simulate such a foundation. If you don't add a foundation, you could end up with something like this image where the structure appears to be floating above the ground.
When you're working on your Master Builder - Structures certificate, don't forget that you have one bridge to build. The requirements don't say anything about the kind or the size of bridge that you have to build, only that it should be prototypical. A short bridge like this one, which is on the N scale layout of a friend of mine, would work wonderfully for this requirement.
When you build your layout's city center shopping district, break up the walls on some of the storefronts to recess the doorways. In colder climates, this was often done to provide customers with a place where they could make necessary adjustments when entering or leaving a store to account for the weather outside. The DPM kit shown here already has the doorway molded as a separate piece so adding a couple walls is a trivial matter, but don't be afraid to cut into the kits you're building to add such an alcove. Sometimes the doorways could be recessed as far as 10 feet with large sheet glass windows on the sides to give the stores some additional display space. Look around your city's shopping area and use your imagination here.
Some modelers just don't have the time to build the exquisitely detailed castle including every last brick in the walls and a drawbridge made from individual planks. If you look at it right, you can see a castle in the most mundane of materials like this packing remnant. Remember rule number 1 - "This is my railroad" - and never forget the unwritten rule number 3 - "Always have fun with the hobby."
When you're assembling a kit structure, spend a little extra time to make sure that all the parts fit snugly, even going so far as to fill, sand and paint over any gaps that result from assembly. A seam like this one will definitely not help you in merit award judging.
Adding interiors to your foreground structures can not only get you extra points on NMRA contest judging, but their presence on your layout makes the viewer believe that your background buildings are also as detailed, even when they aren't. The model pictured here was entered in the structures category at the Seattle convention.