After previously talking about evaluating ERA, it's time to turn our eyes to the always sexy strikeouts. For fantasy purposes, you'll rarely make a huge investment in a pitcher unless he can strike people out early and often. Being able to accurately predict whether a pitcher will repeat his strikeout totals is an important part of being a good fantasy baseball manager. Unlike ERA or WHIP, there is nobody else behind the pitcher that plays a role in the strikeout so we need to really evaluate the pitcher's skillset in order to evaluate his strikeouts.
These three numbers above correlate well with strikeout rates in a given year. So, if you see a pitcher early in the year with a great strikeout rate but low Sw-Str% and/or high Contact% then you can make the assumption that his great strikeout rate will not continue.
If you really want to dig deep into a pitcher's ability and mindset, there's even data available on the value of his pitch types (curveball, slider, fastball) and how often the pitcher is throwing each and that might tip you off to a change in a pitcher's strategy. A strikeout rate could suddenly bloom when a pitcher stops throwing one of his bad pitches and starts throwing his better pitches more often, for instance.
One thing to keep in mind that can affect strikeouts in an unexpected way is Batting Average on Balls in Play (BABIP). When a pitcher has a very high BABIP, he is getting unlucky as more balls are falling in for hits. This affects strikeouts because that means that he gets another chance for a strikeout instead of that ball hit into play becoming an out like it possibly should have. A pitcher with a lower BABIP may end up showing a reduced strikeout total for the opposite reasons.
All of this data is available on the player pages at Fangraphs, if you scroll down far enough. So, there you have it! You can officially make a solid evaluation of a pitcher's strikeout rates to have an idea of whether they'll remain stable or not. You go, you!