Stock prices reflect what investors think a company will be worth. Future growth is already accounted for in the stock price.  Therefore, what positive/negative news, events, or changes in the cost of doing business (fuel, taxes, interest rates, new products, higher sales, etc.) can affect the perception of value?  The market, you and I and millions of other investors continuously add and subtract these new changes.  No, you and I are not making computations; you and I are watching the reaction to the news from bigger money with bigger and better computers and hundreds of MBAs doing the number crunching.

This is an important question and it is why your stock market is in existence, to facilitate that valuation and provide a marketplace to trade or exchange that value for another...stock to cash for example.

There is much to consider regarding the fundamentals of a stock but none more important than those items that affect earnings.  Low earnings with low expectations for the future equals low stock price, high earnings with even higher expectations in earnings equals a higher stock price.

Price-Earnings Ratio - P/E Ratio

A valuation ratio of a company's current share price compared to its per-share earnings. Calculated as:   For example, if a company is currently trading at $43 a share and earnings over the last 12 months were $1.95 per share, the P/E ratio for the stock would be 22.05 ($43/$1.95). EPS is usually from the last four quarters (trailing P/E), but sometimes it can be taken from the estimates of earnings expected in the next four quarters (projected or forward P/E). A third variation uses the sum of the last two actual quarters and the estimates of the next two quarters.   Also sometimes known as "price multiple" or "earnings multiple".    In general, a high P/E suggests that investors are expecting higher earnings growth in the future compared to companies with a lower P/E. However, the P/E ratio doesn't tell us the whole story by itself. It's usually more useful to compare the P/E ratios of one company to other companies in the same industry, to the market in general or against the company's own historical P/E. It would not be useful for investors using the P/E ratio as a basis for their investment to compare the P/E of a technology company (high P/E) to a utility company (low P/E) as each industry has much different growth prospects.   The P/E is sometimes referred to as the "multiple", because it shows how much investors are willing to pay per dollar of earnings. If a company were currently trading at a multiple (P/E) of 20, the interpretation is that an investor is willing to pay $20 for $1 of  current earnings. It is important that investors note an important problem that arises with the P/E measure, and to avoid basing a decision on this measure alone. The denominator (earnings) is based on an accounting measure of earnings that is susceptible to forms of manipulation, making the quality of the P/E only as good as the quality of the underlying earnings number.

Price/Earnings To Growth - PEG Ratio

A ratio used to determine a stock's value while taking into account earnings growth. The calculation is as follows:   PEG is a widely used indicator of a stock's potential value. It is favored by many over the price/earnings ratio because it also accounts for growth. Similar to the P/E ratio, a lower PEG means that the stock is more undervalued. Keep in mind that the numbers used are projected and, therefore, can be less accurate. Also, there are many variations using earnings from different time periods (i.e. one year vs five year). Be sure to know the exact definition your source is using.

Forward Price To Earnings - Forward P/E

A measure of the price-to-earnings ratio (P/E) using forecasted earnings for the P/E calculation. While the earnings used are just an estimate and are not as reliable as current earnings data, there is still benefit in estimated P/E analysis. The forecasted earnings used in the formula can either be for the next 12 months or for the next full-year fiscal period. Also referred to as "estimated price to earnings".   The estimated P/E of a company is often used to compare current earnings to estimated future earnings. If earnings are expected to grow in the future, the estimated P/E will be lower than the current P/E. This measure is also used to compare one company to another with a forward-looking focus

How much emphasis you will put on fundamentals versus the technicals of the chart is up to you the trader.  Most traders will emphasize the technicals while not totally ignoring the multiple and the current price.  Maybe it would be best to wait for the top and consider shorting once it breaks to the downside proving that it is overvalued...it's your call.