I don't know what the state of your soil is, but it is to late now to mix in some manure which you could do just before winter (for next season). So I would recommend to mix in good compost, worm castings and a mycorrhiza (loads of manufacturers to chose from).
If your in the possibility to do a soil test, do that as it will give you valuable info on what's already in the soil and what the pH is. Depending on that you can estimate the amount of calcium (pH goes up) or peat (pH goes down) that you'll have to add. Also add some perlite to aid in drainage and oxygen availability.
Regards,
Bob