One tip about pricing your BTL rent. Beware the potential tenant who agrees readily to the rent without even trying to negotiate or haggle. They may have no intention of actually paying the rent!
I'd thoroughly agree with the advice to pick people in the early stage of a decent career path. I'd offer a small discount (50 - 100pm) in return for a larger than usual deposit, say three months. They then have an incentive to keep the place in good nick. And get an employment reference and work contact details.
Since getting an apartment back from a heavy smoker that stank of tobacco, I've always put a "no-smoking" clause in the tenancy agreement and specified that a breach will lead to a forfeit of deposit. In practice, I will actually price it higher than my target and offer a "discount" for non-smokers.