Justin,
On "growth" stocks, I use a strict sell-stop discipline. That removes emotion from the equation. I set the sell-stop immediately upon buying a stock (usually at 5%-10% below my purchase price), then re-set the stops once per week. If the stock opens up decently, I widen the sell-stop percentage. My "default" percentage is usually 15%. I keep trailing it along behind the actual price (always up, never down).
On dividend stocks, which I keep in a separate portfolio, I use a buy-and-watch strategy. I hold for at least 6 months, then do a portfolio review to see if any changes are warranted. In my dividend portfolio, I'm looking principally at the continuation and raising of each stock's dividend, plus its apparent safety. I'm way less interested in each stock's price than I am in its dividend.
Finally, even though I "know you can't time the market," I do compute what I call a Timing Outlook every two weeks. It has 10 components and is meant to be a short-term predictor (a few weeks). If the Timing Outlook is not favorable, it's rare that I will purchase a stock at all, because I like all my stocks to get off to good starts.
The practical effect of the approaches above are:
(1) I've been mostly in cash for most of the year in growth stocks...therefore way ahead of the market; and
(2) My dividend stocks are running a little better than the market, with the portfolio throwing off about 5.1% at the moment (based on my original investment).