Help with a second job inteview?

I have been selected for a second job interview,and the thing is I have been out of work for 4 years due to ill health...I am very nervous as I really want this job as I want to provide for my kids...I dont know the kind of things they will ask me and what answers to give...I feel I may have lost some confidence.How should I present myself?should I practice...i'm just stuck...its on the 5th June....Its quite an informal interview but sometimes that can be harder i think....any ideas or help would be fab please....thanks