I used to use the candle-gazing method of meditation fairly frequently when I was first learning to meditate (and still do, occasionally, when I'm meditating in a room that's set up to allow it).

I tend to find one way to avoid staring at the flame too hard is to allow my eyes to half-close and then just kind of… rest my gaze on the flame, instead of deliberately looking straight at and into it.

I don't know if that might be helpful for other people trying out the technique or not, but I know it helped for me

Blessings

Starfire