I just want to point out a misconception about "splitting your devices evenly across networks" that is propagated in the accepted answer. Under normal usage you should absolutely not do that.
What you should do is simply connect all your "speed-hungry" devices (laptop, tablet, smartphone) to 5 GHz network. It is a faster network with lesser interference. The more devices connected to it → the better for them.
Put all other — not "speed-hungry" — devices (like printer, 'smart-toothbrush', Nest thermostat or whatnot nowadays) on a slower 2.4 GHz network. Don't worry, they will be able to communicate with 5GHz-devices just fine, but keeping them off 5GHz network might help preserve high speeds and low latency for those devices that actually need it.
Nevertheless, the fast 5GHz network has limited range and penetration capabilities, so at some point in your house you will probably notice that devices have trouble connecting to it. This is exactly the point when 2.4 GHz network comes in handy once more, because having good signal on a slightly slower network is always better than barely being able to connect to the fast one.
3Are you asking about the 2.4GHz band or the 5GHz band? – David Schwartz – 2013-01-26T23:44:18.920