Yes, you must thoroughly clean your deck before staining. If you don't, dirt, debris, grease, and mildew can get trapped between the wood and the new stain. This not only looks unsightly but also prevents the stain from penetrating the wood properly, reducing its ability to protect the deck from weather and UV rays. As a result, the stain won't last as long or look as good. Any existing mold or mildew left untreated can continue to grow beneath the new stain, potentially leading to wood rot and structural damage. Always wait at least 48 hours after cleaning for the wood to dry completely before applying stain.

Yes, it's a good idea to sand the wall with fine-grit sandpaper after spackling, especially if you plan on painting. You can do this by hand or using a sander, but the idea is to ensure the spackle is flush with the wall. Sanding will give your wall a smooth, uniform finish and help your paint and wallpaper stay put.

Yes, it is important to wash your deck before painting to ensure the paint applies well and adheres properly. While you don't have to use a pressure washer, it is one of the most efficient cleaning methods. Pressure washing can quickly remove dirt, wood fibers, and flaked paint, getting deeper into the wood than manual scrubbing. You can also clean the deck with a stiff broom and a cleaning solution. Regardless of the method, a clean surface is essential for good paint adhesion. Make sure the deck is completely dry before applying any paint.

Whether to brush or roll stain on wood depends on the project and your preference. Brushing is ideal for smaller, intricate areas and offers more control over the application, ensuring thorough coverage and penetration into the wood's grain. 

Conversely, rolling is efficient for more extensive, flat surfaces and can save time. However, it is not always the best fit for textured or uneven wood. Some projects may benefit from combining both methods, using a brush for detail work and a roller for broader areas. Ultimately, the choice between brushing and rolling depends on the specific requirements of your staining project.