Battery saving advice for iphone 3g(S) running iOS4 ?

Right so my iphone 3g(S) running iOS4 seems to run out of batter very fast , OK I play the odd game here and there I also use WI-FI to look at emails and facebook . My screen brightness is pretty much all the way down , it goes into sleep after 1 minutes though i always press the button myself to lock it before then .

I know there are apps out there some free ( all include adverts ) and some paying for something like 59p to buy it , I don’t mind spending the 59p for a small app that could save me alot of time . But before buying said app i would like to know your battery saving advice and tips , even something as silly as don’t use the phone is welcome :P .
I think my standby time was 19 hours talk times was at around 2 hours and usage time was around 5 hours in total .
Do you experience the same issues , or have you experienced it in the past but found a way to stop it .?
Yes I do a full 100% charge yes I do drain the battery fully , as said above my brightness is already low . I have no wall paper or screen saver and i log out of everything and turn everything off after using it .