When sanding, start with rough grit sandpaper, then move toward fine grit sandpaper. The larger the number is, the finer the grit paper. How fine the grit depends on the project – 220-grit paper is about as fine as needed when hand-sanding.
Remember, always sand with the grain of the wood, not against.
Use a block of wood when hand-sanding, rather than holding the paper against your hand. (Sandpaper tends to conform to the hand, preventing you from achieving a good surface with the wood.) Staple the paper to the block to keep it in place. Once the paper has been exhausted it can be easily removed.
Purchase sanding blocks at a hardware store or home center. Certain types of block have pins inside to lock the sandpaper in place. Pull one end of the block apart to remove the paper and replace it with a new piece.
A contouring sponge has sanding surfaces on all four sides, allowing access to the corners.
If power tools are preferred for sanding, a belt sander is a serious power selection. (Take care not to burn the material while using a belt sander.) The down-side to a belt sander is that it can't get into tight spaces; another tool will be needed for that.
A detail sander is a power tool that allows access into corners that a belt sander can't. It has a pointed end and the sanding pad goes past the body of the sander in order to get into the corner. The sanding pads have hook and loop tape on the back for easy removal.
For really odd-shaped edges, make some sanding sticks. Choose differently shaped dowels and attach sandpaper to them with staples or double-sided tape.
Sponge-backed sandpapers are helpful when working with pieces that have round or uneven edges. If sponge-backed sandpaper is not an option, use a deck of cards to help sand contoured edges. Take the cards out of the box and wrap a piece of sandpaper around them. While sanding, the deck of cards will conform to the contour and allow access to those difficult spaces.