My Hart research started off with the marriage of Sarah Hart to William Olley in 1813 at Chelmsford, the marriage and a census gave me a clue to Sarah. I found the marriage of Sarah's parents, Samuel Hart and Ann Clark, I think, from Jack Baxter's Essex Marriage Index. Armed with that and some clues from the IGI, I was off and running (at times more like stumbling), luck also played a big part, the Family Search site was a big help with the Hart family, using the IGI, Ancestral File and Pedrigree Resource File there was a wealth of Hart info to check through. There are also a lot of Thaxted Harts on the IGI but I haven't linked to them yet.
I usually get over to the UK and Essex every second year, this is when I confirm (or not) the IGI and other clues and take them further in the PRs.
In the ERO they have a set of volumes which contain indexes to baptisms and marriages, they are very useful, have a word with the duty Archivist he/she will show you where to find them.
My stumbling box has been and still is, finding the marriage of Alexander Hart and Elizabeth circa 1745 or possibly earlier, fortunately it hasn't stopped my Hart research.
Currently I'm also looking for the marriage of John and Jane Hart circa 1689, They had two sons named John baptised, one in 1692 (buried 1696) the other baptised 1697, both the baptisms and burial were at Panfield. According to the IGI there was also a Jane baptised at Panfield 1689 but I couldn't find her.
By the way don't be too hasty in dismissing census finds because they are a year or two out, ages given in the censuses are often out and somtimes way out.