An uptrend is identified when there are higher highs and higher lows as time passes; A downtrend is identified when there are lower highs and lower lows.
Another thing to look for is channels. Channels are comprised of two parallel trend lines with prices bouncing between them. The typical strategy is to sell at the top of the channel and buy it at the bottom of the channel.
Channels provide a context in which high-probability patterns are identified. In addition to trading with the trend, traders may sell off of the top of the channel or buy off of the bottom of the channel regardless of trend direction. If a pattern (Gartley, butterfly, etc.) converges with a trend line, it greatly increases the probability of a successful trade opportunity.