Hello! My GP advised that ideally you should start taking folic acid at least 3 months before TTC.
In the UK the recommended dosage is 400 mcg per day - but this is lower that in most other countries (you can buy separate folic acid tablets or prenatal vitamins i.e. pregnacare etc quite often have 800 mcg in them)
You can't really hurt yourself by taking more than the RDA - your body will pee out what it doesnt use.
If you fall into certain catagories you might want to take some advice as to how much folic acid you should be taking - i.e. you might need to take more if any family history of neural tube defects such as spina bifida etc, if you have issues such as chrohns disease or IBS etc.
If you want ALL the fact on folic acid take a look at the thread below - there are some amazing folic acid experts in there!
https://www.babyandbump.com/trying-to-conceive/152279-folic-acid-truth.html
Generally though before TTC (aside from folic acid) it might be worth getting your immunity rubella check out a minimum of 3 months for - just in case you need a booster.
Other than that...good luck and enjoy!