To determine if the entire surface of a board that you've run through a thickness planer is flat try the following: Scribble a chalk mark on the surface of the board. Then run it through the planer until the chalk mark disappears.
The problem with plywood is getting in from here to there. It's heavy and getting a good grip is difficult...especially if you have to carry it for any length of time. An easy solution is to take a couple of C-clamps and tighten them on to each end. This will give you the handle you need to get a good, solid grip.
When building a deck or other outdoor platform, don't use lumber wider than 6 inches. Ponding water on wide boards can lead to eventual cupping problems. For example, use two 2x6's instead of one 2x12. Pros advise installing the boards crown-side up to help minimize cupping and shelling of grain layers.
When purchasing lumber, know the various grades. Often perceived savings can be the result of a lower grade wood.
When going to buy lumber, eliminate the guesswork by taking along the right gear. Take a good flashlight to be able to see wood in dark lumber sheds, plus a pocket knife to scrape rough-sawn boards to check grain. Also take along a good measuring tape, small square, pencil, notebook, and a pocket calculator if you will need to do much figuring.
Your building materials supplier should make random checks of moisture content. 7-12% is good for interior finish materials. 15-19% for kiln dried framing stock.
When removing the grade stamp from lumber, apply paint thinner before using your sander. This will help take out the ink from the wood.
When using treated lumber in landscape retaining walls, apply roofing tar to the ground contact areas.
If your smaller projects call for clear pine without any knots, you can save money by buying a lesser grade, then cutting out what you need from the clear areas between the knots. Also, when buying wood, remember that face grain is not critical for structural parts which won't show. You can likewise save on lumber costs if you can use shorter or narrower boards, or if you only need one good side of lumber for your project.
To conveniently store drywall, paneling, plywood and other long boards, build a second wall out about 2 ft. from a shop wall. Behind this new wall you can store panels, or you can use the space to build shelves as needed to house long dimensional lumber. But build enough shelves for long boards so you don't have to unload a large pile to get to a board near the bottom.