What are the best strategies for winning at online poker?  For
instance, are there "tells" that apply online, or tips like looking at
whether or not people are autobidding?  What are the best online poker
games to play (hold 'em, omaha, etc.), what are the best styles
(straight games, tournaments, etc.), and what are the best types of
betting (no limit, pot limit, $ amount).  Are there best times of day
to play, and best betting levels to optimize my chances?

This might be helpful:

http://www.playwinningpoker.com/guides/internet.html

I was cruzin? by, so here are a few quick notes: Remember, online
poker is designed to earn the company money, and not much else. I
recommend: Become a good ?real? poker player. Read books published by
2+2 Publishing (Sklansky, Zee, Malmuth, etc.). Whatever you choose to
play online, you have to play even tighter than elsewhere. I have not
played online in many moons, but when I did, I found it barely worth
my time from a money standpoint. We play locally, and at the casino (2
hr trip). Hold ?em: Play only super-premium cards, and FLEE tables
with lots of pre-flop raisers/callers (pot limit or no limit). Omaha:
I can?t play ?hi?, but I can play hi-lo in my sleep - play ?nutty?(pot
limit or no limit). 7-card-stud: This is ?almost? a real game online,
especially at higher levels, but you have to play SOLID SOLID SOLID
(by the book)?most people simply cannot play that way; if you can?t,
then stay away. With all games, I think higher limits are better. Play
against people who you have watched play and know how they are
playing. Play against suckers, and flee from tight players/tables. If
you can?t win consistently, FLEEE! Oh yeah, Wilson Software makes some
good learning tools. Have fun! Don?t go on tilt - haha.

I have to respectfully disagree with nearly everything the previous commentor said.
Online poker is it's own game.
Lots of B&M players come online thinking they'll cleanup, bust out
because the fail to adapt properly, and then complain about online
play.

Pay attention to the information your opponents are giving you.
In online, that's basically limited to betting patterns.
remember how people bet, are they in every hand, or selective,
do the always limp, always raise, only raise pairs..
do they get aggressive when on a draw or only come strong w/ the nuts.
are the passive - bet out preflop & fold quickly to a bettor.
or will they call you down to a show down no matter what? - don't
bluff these peopel, keep it ABC when facing them.
are they the kind of people that fish for a straight when they get
ahold of any 2 connectors?
these & many more are all valuable things to take note of.
after 20 minutes or so, if you've paid enough attention, you should be
able to successfully place people on what hand they're working know
when to re-raise them, when to lay down to them w/ a fair amout of
consistency.

the lower stakes tables will have more fish, high stakes will be
people playing at a higher skill level - just like a B&M casino.

I prefer pot-limit & no-limit Texas Hold'em, but that's just personal preference.

AVOID PARTY POKER
I recommend UltimateBet.com or Pokerstars.com

I personally don't like the 2+2 books.
David Sklansky teaches super tight, straight forward ABC poker, which
really only turns you into a mediocre player.
avoid any book labeled "super system" best to learn the guidelines,
understand them & develop your own system.
just copying someone else will get you nowhere since it's impossible
for them to instruct you on every situation you'll encounter.

I recommend TJ Cloutier & Tom McEnvoy.
read anything they write.
Ken Warren also isn't bad for a beginner