Zaistev's Rule

The more substituted alkene:

CC=CC

is generally preferred over the less substituted alkene:

C=CCC

when reacting for example haloalkanes:

CC(Br)CC

in E2

Notes

Products that don’t obey this rule are called the Hofmann Product or minor product.

Mnemonic

Zaistev’s product has an s in it because it is more substituted
Hofmann’s product is off, man (off to the side)