Try getting an Auto-focus lens if you can. They're more pricey, but definitely worth it. Shooting at f/1.8, it's quite tricky to get properly focused when doing it manually - I can never really tell through the view finder, or even on the screen as to whether it's fully in focus; it's only when you put them on a computer screen that you can really tell.
Here are some from my D5000 + 50mm fully manual Nikon "Series E" film lens.. (all shot at f/1.8)
Also worth noting, if you get a film lens like mine, you can only use it in Manual mode on the camera and you have to adjust aperture on the lens itself - the camera doesn't recognise it's got a lens on I don't think?