“You say to-may-to and I say to-mah-to” may be dismissed as a light-hearted line from the song Let’s Call the Whole Thing Off (written by George and Ira Gershwin for the film Shall We Dance, since you asked), but it makes a serious point for writers.
How does your character speak? Are they quietly spoken or brash and loud? Do they have a vocal tic? A regional accent? Are they from another country?
Whatever you decide, how can you get this across to the reader? Some writers go all out, dropping aitches and adding apostrophes willy nilly – but will this help or hinder someone who is trying to engage with your story? Deciding to be true to a dialect may be authentic, but do you really want to add a glossary of words and phrases to the million jobs you have in store?
At the other extreme, unless you’re creating a period piece, having every character speak in the stilted tones of the 1920s isn’t going to enhance the reading experience either (or should that be eeether?). After you’ve written a page of dialogue, speak their words – maybe get a friend to read their words aloud too – and you’ll soon grasp what is working and what doesn’t feel right.
Of course, the to-may-to/to-mah-to debate also throws up another question – are you aiming for a British or an American audience? I’d advise you to make that decision before you’ve typed the first word of your manuscript – and then stick to it.
I am the social media editor for W42ST magazine, which is based in New York City and I know how difficult it is to get into the US frame of mind when you’ve been writing solely in British English since infant school – but don’t panic. Google is a great friend, and there are some really useful sites to advise you when you’re stuck.
Here‘s some recommended reading…
http://www.tysto.com/uk-us-spelling-list.html
https://www.spreeder.com/important-american-and-british-spelling-differences-you-should-know-2/