Spoiler

Find a co-aligned altar (white if you're L, grey if you're N,
black if you're C). Sac a lot of gold or monsters, you will
first recieve a message like 'you feel like your diety is very
close to you'. You must sac a bit more though, to be ready to
pray, and recieve your (pre)crowning.

If you are of extreme alignment (L+, N=, or C-), your message
will read 'absolutely close', and you will get crowned upon
praying. If you are not of extreme alignment, your message will
read 'extremely close', and you get precrowned upon praying.

You are also limited by the exp. level of your PC, in relation
to the number of artifacts you have generated. You must be at
or above exp. level 8 + (3 times the number of artifacts generated),
in order to be elligible for pre(crowning). So limiting the
number of generated artifacts, is a good idea.

Note, there is sometimes a display bug, that might mess up your
efforts to precrown at a neutral altar. Saccing at a N altar,
draws your alignment toward N=, and if you aren't careful, you
might accidentally get crowned instead of precrowned. I think
hitting the '@' key forces a screen redraw, so you can make
sure of your alignment first.