I'm really getting on a but. I have no single piece of advice!!
Nobody has written a book about you and your baby (HV)
Never be financially dependent on anyone else (DM)
Don't spend more than 1/3 of your income on mortgage/rent (DM)
Don't do something you love for a living, it will become a chore, and you'll no longer love it. But do find something you enjoy (my late, great dad).
Whatever your child is doing, good or bad, it's just a phase. Don't get too despondent or too complacent. (Woman I met at a navy group the first time I left the house alone with a baby).
Be yourself - my old boss/now very senior manager in a large organisation, when I bumped into him the day before an interview for a job I really wanted. I got the job.
Take it. It's not your first choice, but you need to move on. No one will care what your A level results are by Christmas (my head of 6th form; I had a difficult home life).
And I'm not at all religious or very spiritual,,but DM has the Serenity Prayer on the wall by her bed, which I rather like:
Grant me the serenity to accept the things I cannot change,
courage to change the things I can,
and wisdom to know the difference.