Tips in no particular order:
Bricked-in windows – When modeling windows that have been bricked in, us a slightly different color for the filled in area and possibly offset the motar lines.
Cheap Z Scale Vehicles – Charms used on charm bracelets make great low cost vehicles, costing as little as $1.99 each. Cut of the attachment ring, paint, detail and you have a nice low cost Z scale vehicle.
Epoxy Aid – For irregular & difficult attachment problems, consider a “rope” style clay-like epoxy like QuikSteel (available at auto stores). Cut off a piece, kneed it with your fingers, roll in a ball and apply. It will fill gaps & allow for leveling.
Field Grass Homemade – Take some Woodland Scenics(tm) Field Grass and make a small bundle. Cut one end to get the length you want with the other end leave random lengths. While holding the bundle, put a drop of CA on the end you cut. Use CA Activator to speed up the drying process to a few seconds.
Ground foam applicator – Save small plastic milk jugs from fast food places. Drill holes in the top, label the contents, and use for applying foam with more control.
No Spill Liquids – Take a 2″ thick piece of foam 2″ x 2″, cut out a hole in the center the size of the liquid container. Place the container in the hole and if will be harder to knock over and spill the contents
Paint Faster – Use a squeeze bottle to store & apply paint to landscape. You don’t have to dip the brush in the paint can & remove the excess – just sqeeze & brush.
Spray Paint Cans (From Scott P) – Label the color of the paint on the can lids & cans for easy idenfication when the lids are removed.
Static Grass Flocker – Make your own for about $40. using “How To” from the web.
Weights Light on your wallet – For cheap weights save your tin cans (I use dog food cans) and fill them with Sackcrete motar mix (mixed according to instructions). They are great for holding down track while the glue dries.