I don’t know how knowledgeable you are about grammar; personally I stink at it, I don’t understand it at all, but I have picked up a few things along the way.  For your own education, here is a quick note about then.  Or than.  Do you know the difference?

Funny I used that word, difference.  Then is for time purposes: ‘She raked and then mowed the lawn.’  ‘Then the dog suddenly pulled on the leash.’  Then is used to describe an action taking place after the aforementioned.  However, than is about difference.  ‘That is better than this.’  ‘She ran slower than him.’

It’s important not to get too carried away, but little things like that make a big difference.  So learn little rules.  Go in from the moment you start the book armed with simple knowledge and you’ll have less work in the editing process.