Someone who pays attention to someone else's feelings outside the bedroom are likely to do exactly the same inside it.
As Cosmo explains: "A guy who responds to feedback - faster, slower, softer, harder, and so on - will get a real orgasm out of me. Every woman is different. There is nothing worse than an 'I'll show you how it's done attitude.'
You are a good kisser
As someone on Reddit explained slightly more crudely: an aggressive, clumsy kisser is also likely to be the same in the bedroom.
You are spontaneous
Someone who is spontaneous and willing to try everything once is definitely a good sign. As relationship therapist Pepper Schwartz explained to Women's Health magazine:
It's hard to be good in bed if you only do what you know and don't do anything but that
You are confident
“Confidence is so sexy, and women who exude higher self-esteem in other arenas are likely to carry that confidence into the bedroom,” says sexologist Jessica O'Reilly.
And one (slightly weird) bonus sign...
You are good at petting cats
According to LordResonant: "A man who's good at petting cats is probably an attentive lover. Some people just like to maul their fluff. If the cat is purring and clearly loves it, it shows that the guy is good at paying attention to what another creature likes (and will probably do the same in bed)."