Step 1: Make or acquire art
Most cities will hold artists' open studios, where you can walk around checking out neat art, meeting the artists, and generally poking through interesting live/work spaces. This means you can find work by young/unknown artists, who are usually much less expensive than big-name artists yet often just as talented, and that you don't have to pay exorbitant gallery markups. Get out and look around- meet some neat people, support a starving artist, and get inspired to make something yourself.
I found a neat piece by Emily Keyishian. You can check out her art during the SF open studios every October, or as listed on her website. Of course, this picture needed an equally impressive frame. Having spent all my money on art, I got to make the frame myself.
Step 2: Select wood
I wanted a rich, deep brown wood to bring out the brownish bits of the oil painting. We went to PALS in Oakland, CA, and got sustainably harvested Chechen, a Central American hardwood. The boards were planed but needed to be edged, so I made sure to select boards wide enough to accommodate my needs after the edges were trued.
Step 3: Trim lumber
The edges on the boards were quite rough and the boards themselves were not square, so I needed to be sure to trim along the entire length of the board. To square the boards, I judged by eye which side was straighter, put this side against the table saw's straightedge and made a cut just deep enough to cut at least one blade width over the entire length of the boards. I then flipped the board over, adjusted the straightedge to to cut another blade width narrower and cut this side. By doing this, the two long edges of the board were now parallel and straight.
Make sure to move the wood smoothly through the saw, as pauses may allow the blade to burn the wood.
Step 4: Cut boards
Step 5: Sand boards
Sand the surfaces smooth, removing burrs and saw burn marks. Start with coarse grit, (~100) and move up to higher grit paper (200-400). After the frame is assembled, you'll finish the wood with hand-sanding of even higher grit paper.
Step 6: Measure and mitre cut
This is a serious measure-twice-cut-once situation: it's very easy to accidentally make your angled cut the wrong direction, or to measure length from the wrong side of the cut. Always measure from the inside, or shortest side, of the piece; this will be the side directly against the picture. I find it useful to pencil in a line in the direction of the angled cut to make sure I do it properly. Drawing in these lines and doing a mock-setup of the uncut wood is a nice way to double-check, especially if you're new to the process and/or paranoid about wasting the yuppie timber you've purchased.
Step 7: Prepare for biscuit cutting
To prepare for biscuit cutting, first identify the size biscuit you'll use and where it will be located. The hole you cut will be slightly larger than the biscuit itself, so make sure you position the biscuit cut appropriately. Sketch in the location of the biscuit cuts, as they're another one of those points of no return.
Clamp your boards down firmly to your work surface, positioning them for proper attack by the biscuit joiner. Mine cuts horizontally, so I clamped the wood down as shown below. Since the pieces of wood are small I clamped two together to help support/stabilize the biscuit cutter, oriented such that I could cut the outside edge of both pieces.
Step 8: Make biscuit cuts
Butt the cutting surface firmly up against the wood, match the center line with your mark on the wood, and hit the trigger. Congratulations, you've made a cut!
Step 9: Assemble frame
Now's a good time to find that wood glue; this is a cheap product available most anywhere.
Step 10: Glue
Try not to smear it all over the good bits of wood, as you'll have to sand it off later.
Step 11: Clamp
If you've got some of those fancy right-angle clamps this is the time to use them. If not, get a couple of those ratcheting tie-downs, enough to encircle your frame, and loop them around loosely. You'll need to pad the corners and the ratchets to prevent damage to your carefully-prepared wood. You can use several layers of cotton cloth, paper towels, or the like; just remember that overdoing it is preferable to underdoing it.
Cinch the tie-down into place, then rack the frame (wiggle it side-to-side) using your straight-edge to figure out when you've got the whole thing square. Measuring your diagonals can help- they should be of equal length. Once you've got the whole thing situated add a bit more glue to the biscuit joints to be certain they'll seal solidly.
Homemade tie-down clamps would have been good here, but the ones available didn't quite fit.
Step 12: Hand-sand
You'll need a variety of grits: I gave the biscuit tips a once-over with 100 grit to create a smooth surface, then hit the entire piece with 220, 320, then 400 grit. Sand with the grain, and wipe clean with tack cloth* between sandings. I probably should have given the surface another hit with 800 grit paper, but was getting sort of tired at this point.
*The microfiber tack cloths are preferable to the gummed versions in many ways: they're reusable after washing, and aren't covered in nasty gummy goo.
Here's an Instructable on removing sawdust.
Step 13: Oil
Use cotton cloth rags (chopped-up pieces of old clothing work well) to apply the oil. Work with the grain, making sure all surfaces are evenly covered. Let the oil penetrate for a bit, then wipe down your surfaces with a clean rag. The more layers of oil you apply the deeper the shine your wood will develop. I applied something in the 6-8 coat range; go until you're bored and the wood looks gorgeous.
Sit the frame on nail boards to reduced the surface area in contact with the fresh oil.
Step 14: Align frame
Step 15: Align brackets and pre-drill holes
Flip the picture and frame over, and set them on some sort of padded risers. I've used towel-covered milk crates. Make sure you're not going to damage the surface of the painting, then carefully re-align your picture within the frame according to your previous measurements. Position the L-brackets so the ends sit over the frame without protruding, and the angled portion sits over the stretcher.
Chechen and other dense hardwoods definitely need to be predrilled to avoid splitting, and it certainly won't hurt the softer wood of the stretcher. Select a drill bit slightly smaller than the screw you're planning to use: the bit should be the width of the screw minus the threads, since the threads still need to catch in the wood.
We'll predrill and screw the frame first, then move on to the stretcher; this will make sure everything fits nicely without shifting. As you drill, don't push too hard, and make sure to back up frequently to break and remove chips that will otherwise clog your drill bit. Also make sure you're drilling perpendicular to the wood- any additional torque on the drill bit can cause it to snap when you're working with an extremely hard wood.
I'm stressing this because Chechen turns out to be really hard- I broke off a drill bit and a screw when attaching the L-brackets.
Step 16: Sink screws
When you've got the L-brackets firmly secured to the frame, triple-check your picture's positioning within the frame, then drill holes in the stretcher. Make sure you don't do anything brilliant like drill through the front of the canvas- that doesn't improve the artistic value of the painting.
Now sink the screws. You'll probably be picking the picture up as you bear down on the screws, so do this carefully! Alternate between the two screws at the corner, gently tightening up on each until the picture fits snugly. You can finish the tightening by hand if you're paranoid.
Step 17: Attach hanger
You may have planned more sensibly, in which case you'll need to pick up one of those picture hanging kits from your local hardware store, or at least a couple of d-rings and some wire. Attach the d-rings to the frame (or stretcher) about 1/3 down from the top of the picture, and leave the wire loose enough to make a decent arc behind the picture but not enough to protrude over the top. This isn't terribly complicated. Wrap or tie off the wire in secure fashion.
Step 18: Hang and enjoy
Get out your measuring tape and center the picture between whatever architectural parameters you're working within. Now combine your horizontal measurement with the previous vertical one, and make a nice X.
Place your picture hanger of your choice right on this X. You'll probably need to check whether it's on top of a stud or not, and know what kind of walls you've got. Mine are standard wallboard with wooden studs, so I prefer to use heavy-duty drywall anchors for anything but the lightest pictures. Since I'm in an earthquake-prone area I add a large washer to prevent the picture from hopping off during tremors. You can get earthquake hangers, but they're expensive and I've yet to see any more than marginally better than my solution.
Now, put your picture up on the hanger and enjoy the art. This makes the walls seem warmer and friendlier, and having real, properly-framed art on the walls may fool people into thinking you're an adult.
This picture was painted by Emily Keyishian, an awesome artist with a studio in SF's Mission District.