normaly if they take 2+ days to text/e-mail me back i drop a little somthing like this:
1)'hey girl stop playing hard to get, talk to me "wink" '
or
2)'hey just saw a 'drop in somthing relavent' and got me thinking about you, don't be a stranger, talk to me

'
when i say 'drop in somthing relavent' i mean somthing that has happened between you and her that will make her laugh for example i knew this girl who thought a blackbird was watching her so i said:
'Hey this black bird was looking at me and it got me thinking about you, how you been?
talk to me girl, dont be a stranger

'
if you cant think of anything to drop in then you need to bust her on more things
if 2 days go past and they dont text/e-mail back i move on.
you can use 2) first then 2 days later 1) but you will have to step you game up when meeting up to recover.
hope this helps.