Extra prep needed for straights?
When shaving with a safety razor, some get away with hardly any prep at all. Splash water in the face, slap some foam out of a can on the face and shave.
Not the best shave, but some people do it.
With a straight razor that would certainly result in a lousy shave.
At the very least, I wet (usually wash with some soap) my face with a sponge/wash cloth to let the skin absorb some moisture, then apply soap/cream with a brush and whip up a nice dense lather on my face before I start shaving. They key is to allow facial skin and stubble some time to absorb moisture and soften.
Above prep may not be strictly necessary for a shave with a safety razor, but it will certainly make for a better shave.
In order to properly answer your question, we would therefore need to know what your current preparation routine is for a shave with a safety razor.
Lastly, is a shower before a shave necessary?
No; not if you follow above routine.
But if I shower anyway and need a shave as well, I would rather shave after the shower than before.
B.
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