I keep a calculator in front of me at all times when playing to calculate profits, costs, amount of items to gain x amount of xp, etc. I have progressed to becoming more of an xp person rather than an independent person. For example, now, to get my smithing levels up, instead of mining my own coal, and taking a bit of time, I mine pure essence and sell it, then buy the coal. I figure i can get more than 3 pure ess in the time it takes me to mine 2 coal. (2 x 194 gp) < (3 x 150 gp)