Stop flat hair?

[twocultures]

Anyone have any tips or hair style ideas for how to manage my hair between washes and stop it looking so flat all the time?
I have long hair (at the back it reaches just beyond my bra) with a long fringe (chin length) I also have quite a round face even if I'm skinny and if my hairs flat or I have it all scraped back in a ponytail I look really chubby. Also I have quite a big forehead (not huge but big) if I try to e.g. do the puffy thing in the middle when I have the rest up in a ponytail I look really dis proportioned.
I can usually just straighten it on the first day of washing as its still soft and with volume but on day2 it's all flat and I usually don't have time to curl it or spend ages on it and on day 3 I don't even try it just goes straight in a ponytail.
Last time instead of straightening it I sort of "crimped" it with my hair straightener and put some salt spray in and it looked quite nice (and beachy) but next day still went flat at the top.

I definitely suit messy or curly hairstyles and/or braids more than straight hair.
Does anyone have any easy + quick tips to give me some extra volume? Or maybe some super easy braids I could do - I'm really bad at any sort of braiding (continuous unsuccessful attempting of fishtail braids will be the death of me) but could potentially manage something very simple.

Sorry if this post sort of rambles but I'm not very up to date with anything ATM so any advice would be appreciated