"First, do no harm."
Don't teach letter names. Don't get her to sing the alphabet song. Don't teach upper case letters.
Get the Jolly Phonics workbooks www.amazon.com/Jolly-Phonics-Workbooks-1-7-Lloyd/dp/1870946502?tag=mumsnetforu03-21 and go through them, focusing on sounds not letter names! Teach sounds correctly--/s/ should be a hissing sound, not "suh." /f/ is like a puff of air, not "fuh." Another PP has already posted a link about the correct way to teach the initial sounds. It's impossible to completely avoid adding an "uh" sound to some consonants like /g/ and /b/, but try and keep the "uh" as short as possible. You want to try and get your child to understand that these letters stand for a single sound, not the sound and the vowel that comes after it.
You should also try some games to help your child "unglue" sounds in words. "Touch the chair! !Touch the table! Touch the pen! OK, now touch the b-e-d. Touch the b-oo-k. Touch the l-a-m-p." Note that /oo/ in the middle of "book" is a single sound. Kids find this kind of glueing/unglueing of sounds hard at first. Be patient and keep it fun.
As a general rule you are better off teaching nothing at all than teaching your child erroneous stuff that causes problems later on.
Don't be "that parent" who teaches their child to helpfully yell out letter names and write IN ALL CAPS LIKE THIS, so that their teacher then has to spend the next year or so trying to stop the child from pUttInG RaNDom cAPs in half their words, or correcting misreadings and misspellings, like reading "bed" as "beed" because they say an "ee" sound out of habit whenever they see the letter e, etc.
That said, if you can do the above correctly, you can give your child a good foundation and help them stay on top at school.
Understanding how reading works will also help you to keep an eye on what the school is doing. Unfortunately, schools don't always do a good job of teaching reading, because ITT varies wildly and often does a pisspoor job of teaching the actual science of reading, and because older generations of teachers were trained during the "mixed methods" era (a bit of muddled phonics, a bunch of crappy old spelling "rules" that don't work, plus a lot of "looking at the pictures and guessing"). Contrary to what one poster here suggests, reading "Memorising word shapes, finding words within words, using sentence clues, looking for pictorial clues" is NOT how children are supposed to be learning reading.