First, definitions in brief. Special revelation refers to God's disclosure of Himself by an act of direct revelation, such as to a prophet or apostle. This is mediated to us today through Scripture alone. General revelation is God's self-disclosure through the created world.
A locus classicus featuring both is Psalm 19, where the first six verses focus on general revelation, and verses 7-13 deal with the excellencies of special revelation. Remember:
To the choirmaster. A Psalm of David-- snip --
The heavens declare the glory of God,
and the sky above proclaims his handiwork (Psalm 19:1)
The law of the LORD is perfect, reviving the soul;The content and intent of each is different. General revelation shows that there is a God, and that He is powerful (Romans 1:20); special revelation reveals His character, nature and will (Psalm 19:7-13).
the testimony of the LORD is sure, making wise the simple (Psalm 19:7)
Now, HSAT, let's pose a question: is the sola scriptura position, with its affirmation of the sufficiency of Scripture, a rejection of general revelation? For instance, when a sufficientist/non-Jabberwockian/whatever refers to the facts of history, is he de facto denying the primacy of Scripture, and imposing experience over revelation?
Let's give this a bit of consideration. Can you slice the two from one another? Of course not.
For instance, when you say "I affirm the sufficiency of Scripture," how did you do that? Did you learn those exact words from Scripture itself? No, you got them from the realm of general revelation.
"But I got the idea from the Bible," you say, and I agree. But how did you understand the Bible? You read an English translation, right? Did you learn English from the Bible? Not from the autographa, and probably not from a translation, either.
And how did the translators do their work? "From Greek and Hebrew," you say. Yes -- but does the Bible itself translate and explain every Hebrew and Greek word? Of course not; you'd get into an endless cycle there, anyway, since each word of explanation would require a word of explanation, and so on ad infinitum.
No, the most wooden-headed "just-me-and-my-Bible" type has to look up the words of Scripture. He also has to look up place-names, and he has to consult secular history to get any kind of a time-line, and relate the Bible to the rest of the contemporary world. All of these data, all these facts, all this information comes from the realm of general revelation.
General revelation necessarily and by God's design informs and corrects our interpretation of special revelation. For instance, we might read Joshua 10 as teaching that the sun orbits the earth. That is one possible interpretation of the passage. It is general revelation that helps us reject that interpretation, in favor of another. Without general revelation, we might never reconsider our first-impression reading of the passage; but the facts of general revelation require us to do so.
Or to take another, it is one possible interpretation of NT history to think that all of the gifts of the Holy Spirit will continue exactly as-is (or, rather, as-was) until Jesus comes back. Now, I think there are indications in the text itself to the contrary, as I've shown at length elsewhere. But it is a possible interpretation.
It is possible, that is, until we bring in the realm of general revelation, and consider history. Then we learn that there was a sharp break after the first century. To put it mildly, we find that such revelatory and attesting gifts have never again been the norm among Biblically-faithful believers. It is not just hard, but impossible to find any time or place in the last 1900 years where apostolic-level gifts of wonders and inerrant, direct revelation are characteristic.
So general revelation helps our understanding of special revelation.
But the flow goes in the other direction as well.
To take my favorite illustration, let's transport an observer back to the eighth day after the creation of the world. This made-up observer hasn't one datum from special revelation, he only has what he sees.
You ask him how long everything has been around.
He says, "Well, I see one star, so it's all been around at least four years. Then there's this guy looking quizzically at me, and I'd guess him to be around thirty; so it's all been around at least thirty years. And then I see other stars as well, so it has to have been around much, much longer. And then there are these trees, and these rocks...."
Then you hand him the first two chapters of Genesis, and he's faced with a choice. If true, those pages put a different interpretive grid on everything he sees. His impressions were mistaken, because he was lacking some critical information. As Calvin said, the Scriptures serve as glasses for him, enabling him to see and "read" reality more truly and clearly (Institutes, I, vi, 1).
None of this should be shocking or unsettling to the Biblically-faithful Christian. We know that one God created both general and special revelation. Both realms are revelations of the same God. In His mind, there is no clash nor competition. The clash is in our minds, prone as they are to think rebelliously and autonomously (cf. Romans 8:7-8; Ephesians 4:17-19, etc.).
The growing Christian is the person who is learning to live at peace with both, always checking his perceptions against God's inerrant, transcendent, verbal revelation.