buying stocks (market order vs limit order)

[ski]

I am not sure which one to use. It seems everytime I do a market order it is like I get ripped off.

If I am buying insignificant amounts of these stocks (<$15K per stock), want to hold them long term, and am not day trading what do you suggest?

If I place a limit order when should I cancel it? Where would u place the limit in relation to the ticker/bid/ask?

Thx,
Ski