To enhance your scenery try to use dry coffee grounds as track ballast and rip tea bags open and use it as green ground cover. This mixture allows for an excellent texture and incredible color combinations. It is not very expensive at all and works great for HO scale, as everything is very close together.
An excellent tip for wiring is to use terminal blocks under the layout during wiring. It becomes much easier to trouble shoot any issues or add and remove wiring. This can also work for switch machines, wire junctions, DCC modules, basically any area that might need to be noted.
Another great scenery tip for winter mountain scenes is to cut up a cardboard box and paste it together and cover it over with a white sheet that has crinkles within it. Then get a sticky spray glue and toss on dirt, herbs, soot and fake snow to make it look like as real as possible. Adding rocks at the bottom or even larger rocks can make it seem like a boulder. Also, when adding trees, be sure to keep the trees near the bottom or middle of mountain as most of the time the top of mountains does not have trees due to the cold winter.
Buy disposable razors (Bic brand) and use the blade guard for roadway barriers used at construction sites. The razors are yellow; all you have to do is use a black Sharpie to add detail and paint them to use for an elevated track over marsh areas as well. You can also use the hollow handle as chimneys or culverts in HO gauge. The razor handles can also be painted and used to make trestles as well.
Yellow cotton swab sticks can be used as natural gas line pipes. Glue a bundle together for transport and use loose ones for construction sites.
Use electric car outside mirror motors to operate different things such as railroad crossings and anything that has to move slowly for your model train layout. Just have to make up a bell crank with the right ratio and some coat hanger for rod linkage and it looks very legitimate.