I'll throw in my experience so far...
I'm 26, lived here a year, planning on staying long-term. I am purposely not adding a note to my file as I would like to be eligible for instant and quick approvals which, to my understanding, won't be possible once there is a note on there.
I have a bank account without overdraft and a mobile phone contract. I was just approved for a Vanquis card for £500 and plan to charge a small amount each month and pay it in full to build up credit. It'll likely go up to £1000 within about a half year from what I've read...
When my credit report is showing a bit higher score, I am going to open another bank account based on which bank I think will give me the best overdraft. (This really isn't necessary, but I am the type of person that likes having two totally separate checking accounts at two different banks, always have been!) I may also join a credit union. Long-term, I will likely apply for a 'nice' credit card through one of my banks when I think I stand a chance of being approved...