How to build credit rating?

[twoblacklines]

OK I have never had a credit card, mortgaged or used finance. The only thing I have is a mobile phone bill, then the usual rent, insurance tax yadda yadda. I pay for all this either straight out of the bank account online or via debit card.

I want to start borrowing lots of personal credit soon (to be used as director loans in company I own). My credit rating is ~700 which is surprising, a friend told me just to get a CC and it will go up if I pay it off every month.

My question is, what card to get and what to actually use it for? Is there a ratio that works best for building credit?

Can I just pay for my phone on it every month? Which is just £10 a month currently.

Thanks

[twoblacklines]

Thanks for the tips!

Especially the active/dormant one!