Dum, dum de de dum, dum de de dum...
De, dum de de de, de da da da, da da da da, da da... etc.
Thst's the theme music to Crossroads. Basically don't write it like the first five minutes to any episode of Crossroads cos people will turn off.
You need a focal point in every soap. Eastenders has the Market and the Vic, Coronation St has the Rovers. Don't do it completely based around the focal point (a la crossroads motel/hotel they call it now), because you will be restricted for storylines.
Try and convey the characters personality as soon as you can. Make them interesting and of a broad base. Don't have loads of dull people playing bit parts, and put your main characters first, those who are going to be key to the show.
Now, you're writing for the first five minutes, so you won't have to be that in depth surely?. Wrong!
You have to grab your audience by the scruff of the neck but in a gentle manner as though you are leading them into the storyline and not throwing them into it. If you start off with, I dunno a murder or an explosion, it's all a bit too much too soon. If this is the first five minutes of a new soap, as in not broadcast before, then developing a storyline is irrelevant, you have to build your characters up first as they are the foundations for the soap, the plot gets built on it later.
P.S. Have a Cockney bloke in who can only whisper, a pantomime villain character a la Nick Cotton or Terry Duckworth, and someone has to say "Get outta my pub".