Well, it seems you've already found one website.
Seriously, the best thing you can do to improve your fluency quickly is to read, read and read.
BUT (And like yours it's a big 'but' ), you should be readling lots and lots of children's books. English grammar doesn't change much beyond 4th and 5th grade.
The vocabulary, the length of sentences and the number of clauses may increase, but the grammar stays pretty much the same.
Go to your library or bookstore and find illustrated readers for children (preferably ones with glossaries and comprehension questions -- the Oxford series is a great example). Start with ones aimed at BELOW your reading level. (I would guess 4th grade.) Read about 20 of those at the rate of at least two a day. Then move to the next grade level and do the same thing. Continue on with this until grade 8. At this point, assuming you have time, start reading juvenile novels (those written for children ages 12 - 16). Those will take a couple of days to finish each.
While doing this be sure you are keeping a vocabulary notebook and a patterns notebook (write down new constructions as you learn them e.g. "X takes a toll on Y" = X is causing Y a lot of stress or X is causing Y to become worn down or broken") and, most importantly, read everything twice -- once silently and once aloud. After all, what you want is fluency, and that doesn't come without speaking practice.
If you have the money (or better yet, if you can do this at the library) this is a fantastic way to acquire fluency. It has worked for most of my students.
My $0.02. Hope this helps.
- For Teachers