I will be interested to read the answers to this question because apart from regular watering i dont feed mine and perhaps I should but I know that some people use the same liquid fertiliser that they use on their tomatoes.

Yes, tomato fertiliser is good for all flowers and fruit. In general you want a high potash feed for flowers and fruit and a high nitrogen for green growth. If they are in the ground and looking healthy I wouldn't feed them but in pots maybe a week feed once a week or so would help.

I've been using Miracle-Gro. Got one flower blooming on 4 of the 5 Dahlias (2 in ground, rest in pots) I have and lots of buds about to bloom in the next few weeks. I normally add the feed once per week.

Once a week I would say.

I use slow release fertilizer granules all around the garden in spring, then selected flowering plants including dahlias get one or two feeds of dilute tomato fertiliser about now to encourage them.