I applied to tesco once, as a first job. I didn't get to the interview stage. When I applied, I had to do a quiz regarding different in-store situations and what I would do, for example, noticing a spill, or a customer asking for help. I think, if I remember correctly, a lot of them were based on customer interaction. I do think that I answered mine a bit too brutally honest, as I felt absolutely not prepared for the social side of the job. (It was a multiple choice quiz btw). I just wanted to stack shelves and get on with it. Now, after having had a jobs at morrisons i know that I am capable of helping customers.
So I'd say that if you are up for the job, tesco would probably happily take you on. Best thing you can do, is apply, and see how it goes. I can't really advise you on when to apply. As for other jobs, retail can be brutal but can be rewarding if you can move past the (possible) tough parts of it. Everyone has a different experience. Really, just anything that you think you'll enjoy.