Much like porters, there is a lot of room for characteristics of ESB brews. In general, ESBs are characterized by having a medium body, medium to light malt flavor, rich golden color (around 10 L) and are distinguished by a stronger-than-usual bitterness. The bitterness is not to the level of an IPA, but closer to that of the more bitter American Ales. The style is also characterized by a slightly less-than-average carbonation level compared to that of other ales, which is important to remember in the priming process.
The hops used in brewing ESB style beers are in general English varieties, such as Kent Goldings or Fuggles. To achieve the ESB style hop bitterness, the majority of the hops are “front loaded” and added as bittering hops at the beginning of the boil. For Kent Goldings or Fuggles style hops, 2 oz. is generally the norm and these can be boiled anywhere from 60 to 90 minutes. Often, one more ounce of hops is added to the boil toward the shorter end of the spectrum (10 to 15 minutes remaining in the boil) for flavoring hops or as finishing hops (2 to 5 minutes remaining). The dominant hop characteristic in the ESB is the bitterness. The goal is to achieve this but with a level of hop flavor and aroma for balance. To further round out the hop presence, dry hopping is always an option.
A general ESB-style extract recipe would look something like this:
6 pounds of pale malt extract
1.5 lbs 40 L crystal malt specialty grain (adds rich color plus malty flavor)
Bittering hops: 2 oz Kent Goldings (60 min)
Flavoring hops: 1 oz Kent Goldings (10 min)
Dry hop: 1 oz Fuggles
This should produce a relatively medium bodied, richer color, bitter beer while not having an overwhelming amount of bitterness associated with it, but nicely balanced.
If you prime your beer I would recommend removing about a quarter cup of the corn sugar from the normal priming solution process. If you force carbonate I would recommend bringing the force carbonation pressure down to about 11-12 psi.