Three schools of thought. There's the completely American ESB that is basically just an American Amber minus the big late hops, lots of crystal malts. There's the American interpretation of an English ESB (based on the few that are exported) that are strong, and again lots of crystal malts and lots of specialty grains and not much for hops. Then there's the actually authentic Strong Bitter, which is usually fairly simple and gets most of the "malt" character from invert sugar, not specialty grains.
I like the 2nd two. Not so much the first
For the export-ish ESB, I'd probably go 80-85%, about 8-10% crystal malt, both light and dark, probably toss something like Amber malt (or Biscuit, Victory, Special Roast, something like that), and perhaps a very slight touch (no more than an ounce or two) of roasted barley. I don't like the roasted malt in there, but it's got its place. Midrange bitterness for style, easy touch on the late hops. Mashed moderately high. Full, and malty, but balanced. Carb like normal. Aim for maybe 6-6.5%. Carb like normal.
For the authentic, 85-90% Maris Otter, 5% midrange English Crystal and 5-10% invert sugar, on the bitter side of the range, modest late hops, and a light dry hop. Mash low so it finishes dry. Aim for maybe 5-5.5%. Carb it low, preferably on cask.
In any case, as far as hops, EKG or Fuggles are classic, I like Challenger, Bramling Cross is great, WGV, Progress, First Gold, etc. As long as it's English hops you really can't go wrong.