Opinions please!

For the sake of easy maths, let's say I get £700 every 4 weeks.

All bills add up to just under £300 and they are all direct debits.

That leaves me with £400 to play with every 4 weeks, yeah?

Here comes the dilema I was pondering on in the bath... do I double my 3 credit/store cards payment from £25 to £50 every month?  Do I leave everything as is?  Or do I move £300 into the joint account for when either Steve or I need it and still have £100 to play with every 4 weeks?

I can see the positives and negatives to all of them and I'm going to have £1k to play with in the first week of January which is a nice number to start from, so, starting in February 2015, what should I do please?

Any comments are much appreciated and you're free to make up a name if you prefer, I'm just after some opinions is all!  Any thoughts in the comments bit will be very much appreciated!