When you graduate from milkcrates, but cannot bring yourself to buy disposable Ikea furniture for ethical, environmental, or repressed-childhood-memories-of-parents-who-loved-the-Swedish-crap reasons, build some hardwood shelves. Woodworking is often relaxing, and you'll end up with hand-made furniture you can be proud of.
Step 1: Get Lumber
Go to a nice lumber store and get some hardwood. In the Bay Area I go to PALS
and buy certified hardwood. Certified means that the wood was grown and harvested in a sustainable way.
The wood will be measured in board feet. Roughly, a board foot is a measure of volume equal to 144 cubic inches; however, as with any trade specific measurement, it's not quite that simple. Rounding errors need to be dealt with properly
Step 2: Straighten the lumber
The wood will be bowed and crowned. You can fix this with a jointer. Next use a thickness planer to make all the pieces the same thickness. I skipped this step because I don't have these tools.
Step 3: Rip the lumber to the same width
Rip the wood to the same width using a table saw. Make a smooth flat cut on one side of all the pieces. Set a stop just thinner than the thinnest piece and rip all the pieces to the same thickness cutting on the opposite side.
Step 4: Cut the pieces to length
I like lots of low, narrow bookshelves. I usually aim for two shelves 23 inches wide, 12.5 inches tall, and around 8 inches deep. This yields an overall shelf 28 inches tall and 25 inches wide.
Use a miter saw with a sharp blade. A blade in nearly any condition will cut pine from Home Depot, but hardwood is much easier to burn.
I like to hide the end grain on my shelves, so I cut the outside pieces on a 45 degree angle.
Step 5: Layout
Layout the shelves to check all the dimensions and mark attachment points. You can connect the piece with wood screws, but I prefer using a biscuit (or plate) joiner because there are no external marks.
Step 6: Cut slots
Cut the slots for the biscuits.
Step 7: Pre-assembly
Put in the biscuits and pre-assemble to check all the joints.
I use a set of tie-down clamps to avoid damaging the corners of the wood.