re: Poker & As a conservative player, how often shd you play a random (marginal or below) hand?
A major factor in how you play non-premium hands are the playing styles of the 2-3 players to your immediate left. If those players tend to defend their blinds very often or make loose calls then I wouldn't raise as wide from the SB, button, or hijack, if they are nitty then by all means raise with hands that have decent potential post-flop such as 65s, J9, etc. Blind and stack sizes are also extremely important, if you have 15BB and somebody in the blinds has 100BB+, you shouldn't be raising without a strong hand because you're going to get called the majority of the time.
How you've played at the table so far should also be taken into account, for example if you've folded the button several times in a row because of being dealt trash hands you have a good chance of raising and taking the blinds with ATC the next couple of times around because people will think you are actually playing good hands (if they are actually paying attention, which is often questionable in the micros).
In general, if you're going to play non-premium hands you want to always be the first one to raise into an unopened pot (no earlier limpers or raisers). This is obvious but hugely important: if you are the original raiser, you have two ways of winning the pot, but if you call someone else's raise, you have to win at showdown unless you can get them to fold before then.
For newer players I would recommend not playing non-premiums from early or middle positions until you gain more post-flop experience. You're not going to flop the nuts every time, what usually happens is that you flop something like bottom pair or a draw and it takes practice to minimize the risk of losing all your chips in these situations, especially playing out of position.