My car won't start. Tried towing it, when it started, it had to be kept revved up otherwise it would cut out.

I have been having trouble starting the car with the last 2 weeks. It would take a bit to start but then it would be fine, then I Went to try it yesterday and nothing. I tried towing it and it started but cut out again. It gave trouble before with the spark plugs but those were changed about 10,000 miles ago. I was thinking it could be something to do with the petrol getting to the engine or perhaps something to do with the plugs again? I've tried it several times since and still nothing. Hope you can help me out!!!