A Point On Accents

"Well I've been thinkin' about this fer a while and I kept noticing writers who would try t' give their characters accents. They'd wanna go fer Irish 'r Pirate 'r Southern 'r Cowboy 'r Rough-City-Type-Thug, so they'd start leavin' off Gs and Os and Ts and tryin' t' git their character t' look like they had 'n accent. But that did'n' work. I j'st couldn't figure out what kinda accent they were s'posed to be goin' for. The character's voice in my head kept switchin' from one accent t' another."
It's just become a tiny peeve of mine lately. If your character has an accent, decide what that accent is, and then listen to people talking in that accent. Write down every word they say. Try to do it phonetically and be honest to what you hear. But please don't overdo it. I' c'n be very 'noyin' when yer tryin' t' read an' the char'cter's not sayin' English words. Bear this in mind; How do your readers talk?
My reader base is primarily Americans. Most of them will read my words in an American accent. Because of the way Americans often talk they will already read 'going over to the store' as 'goin' over t' the store.' If American English is your native language you'll say it quickly enough to slur some words. So there is no need to slur such words in your writing. If your character is Irish and your readers are American, there is no need to say 'goin' t' the store.' In both languages it's granted that Gs and Os and little in-between letters are often left off.
Instead, only change words insofar as it differs from your readers' native accent. So if your readers are primarily British, pick a narrative accent and let your readers assume that all words are said in that accent unless otherwise specified. If your narrative voice and head voice and out-loud-reading voice are all Westshire, there's no need to make your characters say, 'I fought y' towd me the' wos noi wai t' ge' oiver tha' bridge.' (And furthermore;don't make your characters say things like that if most of your characters speak with a Westshire accent. Just let the reader figure out -through setting, narration, or hints - that the main accent is Westshire. Can you imagine how annoying it would be if you had to read a whole book where the four main characters 'tol' li' this?' It's almost impossible to read.)
So keep changes in dialogue to a minimum.
And finally, know your accents. A great example of an author who did it right is Brian Jacques (Redwall). His characters have a diversity of accents and he presents their dialogue in a way that's fun to read and informs the reader of just what they sound like, without stating the obvious or getting annoying. He's very familiar with the accents in his books so his characters use expressions native to their accents that add a very convincing sense of reality to his characters.