Hi there! Well firstly I wish you good luck with your spread betting. You haven't said how much research you've done on spread betting, but you've definitely come to the right forum. There are many people here with a lot of experience in the subject and you should spend as much time as possible reading as many threads as you can here. Not all of them will be relevant to you, but much of the advice/discussions here should be very helpful to you as a new-comer. Please don't be disappointed if your thread does not receive many more responses, as you must appreciate that over the years, quite a few times someone comes along and says something akin to: "hi, I'm new to trading/spread betting etc., please tell me more"
As for a plan, well the best one is the all too clichéd "buy low and sell high". Sorry... I know that doesn't say much. Alas,there is no guaranteed plan to make money on the punter's side, or everyone would be using it. So, you probably won't find anyone who'll respond to this thread, telling you exactly what steps to follow, and next thing you know, you're surrounded by tropical palms.
That being said, the most important skills are discipline, patience and the ability to accept you're wrong before you've lost too much money. Throwing good money after bad is something we've all done during the learning process. Try to avoid endlessly repeating the same mistake. Try writing down your trades and analysing them later, and the reasons why you took the decisions that you did. That way, you may find it easier, with sufficient time, to develop a structure and method which is most suitable for your needs. And as for demo accounts - there's no substitute to gambling with real money.
Again, have a good read of as many threads in this forum as you feel may be relevant and then consider coming back with some more specific questions and your ideas & criteria. Albeit, you might find that much that you have in mind has already been answered if you look hard enough here.
I'd also recommend you open more than one spread betting account, and spread your business according to whichever serves your needs better as margin requirements, spreads etc. all differ between the firms as regards the various instruments on offer. What may seem like minor differences in spreads or margin requirements over time add up to be quite substantial - and quite often the difference between any given person's overall profit or loss. And I won't go into what may happen if you start winning too much with any one particular firm.
A number of newcomers have found Malcolm Pryor's book on spread-betting to be useful. Lastly, I hope at least some of what I've written was useful for you.