Using trendlines

Trendlines offer a great way to draw lines of support or resistance.

The red (falling) trendline shows resistance and a break out of this is a good reason to buy.
Similarly, the blue (rising) trendline offers support and a break of this is an indication to book some profits.
Incidentally, some stocks tend to have very clear trendlines while some, either because of volatility (or poor liquidity) have extreme spikes which complicates task of drawing trendlines.