Hi,
I work for a very large outsourcing company that processes credit cards for a large number of credit card companies, including the 2 largest.
It is correct to say that every time you apply for a card it shows on your credit rating, as if you are applying for multiple cards rather than just one, so you need to leave any further applications for 3-6 months.
How much you pay off each month is irrelevant to your application, in fact the credit card companies cannot see this information. Credit card companies work on a points system to evaluate your application. Each company has different criteria, as they want to have a particular type of cardholder, a bit like car insurance companies. What they look for is income versus outgoings, payment history - the payment has been paid on time every month and you haven't gone into arrears or over limit, whether you are in permanent paid employment and for how long.
As different card companies have different criteria you should do a bit of reseach before you apply again to see which card suits your circumstances best. What you also need to do is check which bank actually backs the card, for instance MBNA manage Virgin cards and loads more so if you apply for a lot of cards run by MBNA you are actually applying to MBNA for all of them. You can see which bank is running the card as it is usually in the small print at the bottom of the Terms & Conditions. Also BT's between some cards are not allowed, as example if you have a card with Halifax they will not transfer too/from Bank of Scotland as they are the same company.
It is a very complicated industry but I hope thi information helps.