Rather than trying to spell things correctly one letter at a time, focusing on correct vowels/consonants in the first three letters of a word and correct consonants in the rest of the word when possible is the most useful for autocorrect
If you can't spell a word and autocorrect isn't helping you, rather than struggling with it you can leave the misspelling as it is and put [simple definition] in brackets next to it to fix it later
Many words look similar but sound different so listening to someone read your work out loud can be helpful to spot those tricky words
While handwriting, instead of stopping to cross out a letter mid word it can help to ignore the incorrect letter and continue to write the word and cross the wrong letter out after you're done (or lift your pen and start over and cross out the previous attempt when you finish the new attempt at the word)
Dyslexics will often have habits that are unique to them when writing by hand or typing. Common ones are flipping or mirroring similar letters like dpgb, writing a letter like a backwards, shuffling vowels in words like "because," or adding letters from surrounding words. Something I tend to do is add "e" to everything for no reason when a word ends in "n" while writing by hand and putting Ls at the start or end of a word when it belongs in the middle. Identifying your habits can make understanding what you've written later easier.
Sometimes you can get "stuck" on a word that feels like it should be easy to spell because you use it all the time. Taking a break, or even just a deep breath, and coming back to it when you can try again more slowly can help minimize the frustration.
If a word is particularly hard to spell, coming up with a unique shorthand (especially for character names, places, organizations) to ctrl + f and replace later will save a lot of headache compared to misspelling it 16 different ways you need to find and correct later
Learning a bit about linguists and etymology can help you identify the logic of a word a bit easier, like by spotting prefixes to help memorize those "first three letters" that helps autocorrect hook on the right word you're searching for
When learning a word it can be helpful to split up "what it looks like at a glance" and "the literal letters" and "how it sounds" into distinct concepts. If you know what it looks like and memorize how it's spelled, you can use the visual cue to see if you've spelled it right even if it doesn't "look" how it's supposed to [example: decent and descend look like decent and decsand to me, but I know descend has an e so that's enough to get autocorrect to fix it by moving the S]
Neat penmanship isn't particularly important when the letters aren't super correct to begin with imo. It's more important to have space between words, large letters, and high contrast writing. Similarly, the font size and spacing is more important in text documents than it being typed in a dyslexia friendly font. It's not reading, it's writing. Comfort is a higher priority.
You can ask for help even if you don't strictly need it. There's a lot of people who know the struggle of finding the right word who you can ask in writing communities on discord or even just on Tumblr (where answering questions about book recs and other things is super common)
It doesn't matter how slow you go now, you'll get faster over time (and you can surpass peers who don't even have dyslexia) (that doesn't have to be the goal I'm just saying writing speed isn't fixed just because someone has dyslexia)
There's a lot of creative freedom while writing fiction, so you don't have to use words you don't like writing and you can make up words for things that are easy to write
Resting your eyes is super important to eye health, especially with dyslexia which can cause squinting and eyestrain. There are a lot of different eye exercises but a timer every twenty minutes where you take a three minute break to stare out a window and close your eyes for thirty seconds is an easy one to remember
There's no need to spell check the first draft
I hope this helps folks who are having a hard time navigating writing :3