How to obtain more credit?

I currently have 10500 limit across 3 0pc cards. I have used around 7000. I am about to start making 500pm payment to clear one in full in the next 8 months before the 0pc ends. I am wondering, how can I obtain more credit? (For stoozing)

Do I have too much available credit to obtain more? Or will using it all make me look desperate and not able to get more?

I have a good annual income and currently my credit limit is about 25% of my annual salary. Does that play a part?

Thanks in advance for any replies