Power plants in Power Grid
Some mix of the following:


Buy the biggest one you can afford  - Remembering that you have to afford fuel as well.
Try to get a plant that has dual fuel sources
Don't buy a coal only plant if 2 other people already have coal fired plants.
Don't get into bidding wars with more experienced players


If the above isn't working out, switch tactics - save your money and get the cheapest one you can this turn and get a better plant next turn.