First - set your intention. Realize what a protective circle IS and what it protects against. It is not physical and it’s protecting against non-physical entities.
So you you don’t need candles (why? ask yourself what a candle is, magickally - it has nothing to do with protection, does it?) , you don’t need salt (messy, repels insects like slugs - astral beings are not slugs), you don’t need to use Crowley’s Watchtowers (or you will know because you can follow his instruction in his grimoires. You need clear, confident application of your own energy.