Sheldon Brown’s Lock Strategy is often referred to as a preferred method for ease and security. It involves using a mini u-lock to lock the rear wheel to a bike rack between the rear triangle of the bike frame. This accomplishes two things, it secures the rear wheel (2nd most expensive part of the bike) and the frame cannot be stolen unless the rear wheel is completely sawed through. See Sheldon’s page for detail.
In real world situations I’d say it’s not likely a thief is going to saw through your rear wheel, but as this Youtube video shows, it can be done quite quickly. My main gripe about his method is that visually, it doesn’t look as secure as it could.
Lastly, Sheldon’s method does not secure the front wheel. This isn’t a significant issue if your front wheel is bolt on, but most bikes these days use quick release wheels. Sheldon’s method leaves your front wheel vulnerable.
As such, this is my modification of the Sheldon Brown Locking Strategy.
This shows an OnGuard mini u-lock securing the rear wheel, frame (via one chain stay) and front wheel* using a 4′ accessory cable. It is locked to a 2″ pipe, the same diameter tubing used for most bike racks. If you lock your bike like this, chances are it’s going to be the most securely locked bike on the rack. The Kryptonite Evo lock is also very popular. *Note that the angle of the photo makes it appear that the cable is merely wrapped around a few spokes. If you look closely you can see the cable is wrapped around the rim/tire.
To prevent quick release seat theft, remove the seat from the bike and thread the cable coming from the front wheel through the seat rail before looping it into the u-lock. Alternatively, affix a seat leash.