While there are a lot of books that are always on offer cheaply, there are also a huge amount of short term details on better known authors and publishers, and also sometimes even on kindle editions of old books I loved in the past.
I'm a rather obsessive stalker of Kindle bargains. I keep a huge main "Kindle wishlist" and several smaller ones with groups of books for different reasons, but mainly I check my main wishlist every few days and use the sort feature to sort the lowest priced books first. I also use a website called ereaderiq - the UK site as I can't snap up the US bargains. This allows you to see offers in a price range or price drops/books that are available at under £3, under £2, under £1 etc on books which lots of people are watching - so lots of current and recent bestsellers. It also offers possibilities for getting alerts on your wishlist and on favourite authors eg I get alerts for Val McDermid price drops.
Truthfully I buy too many books and would advise anyone newer to Kindle to maybe keep a shorter list and just use that and the daily/monthly deals, and see how you go with those.
You can also subscribe to emails which select a few books from current books on offer at 99p and a couple that are much more expensive recently.
You can also borrow digital books and digital audiobooks from your library - sadly permissions don't let us access these on Kindle erreaders but I have read some on my iphone, and if you find that you're up with night feeds or you have a lot of chores to do for baby and the house, audio can be handy, or you can test out kids' audiobooks on the baby for free, not even bus fares or petrol or the preparations to leave the house if that's a challenge.