After several years out of work, finally getting hired for a job, how soon is too soon to look for a better job?

I don't think I'm going to like this line of work, to be blunt. I did a similar job back in 2006 and only lasted a week before being let go for being "unfriendly." Also, I'm not really using my skills or education to their fullest; I'll be terribly under-employed for what I'm technically capable of, though I'm concerned that the vicious cycle of lack of experience will keep me stuck in jobs like this one (like it has for the last decade).