I strongly suggest not drinking diet soda. :/ Aspartame is a bitch. Weight wise, healthier, but ugh, i hate that stuff. I rather drink the actual product. And they put it in most gum now too. I will stick to my altoid mints. xD
What I do is allow myself one soda of my choice a day, orange juice with most meals (because my blood sugar has been REALLY wacky lately, and my doctors are ignoring it >.>), and the rest water.
And I have started to not eat anything after 8 PM. I will push that back to 6 PM after I adjust my reverse sleeping schedule. xD

Switching the type of bread you consume helps to. white bread is kind of bad for your, but there are healthier choices that taste good. I like wheat bread, and rye bread, as long as it does not have seeds. :/ I have issues with texture.

Getting the right amount of sleep helps too.

And one of the best times to walk is right before breakfast.
Sadly, I haven't had a chance to do this in a while because of college schedule and my backwards days.