Hi Sups, welcome to the forum.
Though one or two people can manage with a keyboard, almost everyone uses a joystick - it makes everthing so much easier. Even with the default stick setup you should find your aim greatly improved, but for best results you will probably need to experiment a bit with calibration: most people find it best to reduce the relative sensitivity towards the centre, to aid 'fine tuning' your aim. It helps a lot to have the plane properly trimmed too.
If you need help with setting up joysticks etc, I'd start by looking at Bearcat's Nugget's Guide here:
http://forums.ubi.com/eve/forums/a/tpc/f/23110283/m/9121094645
Edit: Link problem - Google 'Ubisoft Sturmovik forum' and you can find it there (It is also on the Mission4Today forums somwhere).