Since a p-value is a probability, it will always be a number between 0 and 1. As a general rule, a low p-value means you can probably reject the null hypothesis and accept your alternative hypothesis; a high p-value means your null hypothesis may be valid after all. A p-value of 0.01 would be highly significant, for example, much more so than 0.05 -- which, while still significant, is obviously a much less significant figure.
It also helps if you determine a significance level before calculating the p-value. A significance level is an arbitrary number that represents the probability of arriving at a result by chance. Although there’s no single best significance level, the most typical values are 0.1, 0.05, and 0.01, with 0.05 being the most commonly used figure.
You can use the significance level in conjunction with the p-value to determine the validity of your conclusions. As a general rule, if the significance level is greater than the p-value, then you can probably reject the null hypothesis.