For Maths good website is:examsolutions.co.uk(they explain FP1, M2 and S2 if you plan to do these modules at AS). I would recommend doing S2 at AS, as is not hard, it is pretty straightforward(no complicated differentiation etc.)
For Economics: there are plenty of resources, watch videos on youtube, if possible but Oxford or EdExcel revision guides and also during exams I would strongly recommend learning with specification, as they only include what is necessary. Economics is an essay subject, so bear it in mind.
For Further Maths: For FP1-FP2 look at youtube maths247(explains really good and as well as it explains M1, C1-C4, S1). Btw, I would advise to choose FP1, M2 and S2 or D1(FP2 is pretty hard and is not easier than FP3 in fact and is also A2)
Best of luck to AS students!