Everything above is correct but I'll just add a few points (particularly as nobody has pointed out how lengthy the visa application process can actually be):
You'll need to get hold of a Police Certificate. You'll also need to complete additional documentation (as well as the usual visa application). Further, you'll need to attend an interview in London. All of that takes plenty of time, so you'll need to start your visa application process well before you're hoping to travel.
The the nature of your offence needs to be considered. If it involved 'moral turpitude' the US Immigration and Nationality Act gives the US Embassy no discretion whatsoever when considering your visa application. By law, the embassy staff MUST refuse your application. However you can then ask that it be submitted to Washington as an application for a 'waiver of permanent ineligibility'. The MINIMUM processing time for such an application is around 6 months but it can take much longer. (There's been a post, here on AB, from someone whose partner had two convictions for driving without insurance. He had to wait 15 months before hearing that his application had been turned down).
So the first thing you need to do is to consider whether your offence is classed as 'moral turpitude'. If it involved any form of dishonesty (such as theft or fraud) then it almost certainly is. If it involved violence then it doesn't unless there was intent to kill/rape/rob/commit serious bodily harm or a dangerous or deadly weapon was used. Wikipedia has a useful summary:
https://en.wikipedia.org/wiki/Moral_turpitude#U.S._government_guidance_on_determining_moral_turpitude
If there was no moral turpitude, allow several months for your visa application before booking your travel (which, since you'll probably want to book well in advance of your actual travel date, means applying now for travel in the first part of next year). If moral turpitude was involved you might need to think about making your visa application now for travel in 2017.
From the website of the US embassy:
http://london.usembassy.gov/niv/add_crime.html