I get questions daily about theological issues to which the Bible doesn't seem to give straightforward answers. Over the years I have found three guidelines that help in these situations.
First, it is always best to stick with biblical language. That is, stick to the way the Bible speaks about things. For example, the area of predestination is always hard for us to get our arms around. Sometimes we go too far in our explanations and cause ourselves even more problems. Better to stick with the biblical illustrations such as that in Acts 2 when Peter has no trouble saying that the cross was God's idea, and perfectly planned by him, but those men who crucified Jesus were also responsible for crucifying the Son of God.
Another example would be the current controversy over how good works play into our sanctification. Are we sanctified by grace alone? or does our effort play a part? Again, sticking with biblical language seems to help. Paul gives it to us simply in Philippians 2:12,13 when he exhorts his readers to "work out your salvation with fear and trembling knowing that God is at work in you, both providing the will and the work for his good pleasure." He doesn't get fancy trying to explain the relationship between God's work and ours. He just declares that we have a responsibility to obey and that the power to do so comes from God. In another example of the same tension, he says he "toils, struggling with all his (Christ's) energy that he powerfully works within me." (Colossians 1:29). So the answer to the question is this: I will know that the power of God is working in me when I am working to do the will of God.
Second, it is best to go no further than the Bible takes us. This is so hard, especially given our curiosity and the fact that we're all pretty good at coming up with answers that make us feel better. I have found in my own life, and in my discussions with others, that most of the aberrant theological conclusions we hold are based on assumptions never found in Scripture.
For example, many people's views on things like the eternal destiny of those dying in infancy, the reality of eternal punishment in hell, sovereign election, and a host of other "hard truths" are based on their own sense of what it means that God is love. Despite the biblical evidence that God's righteousness, justice, and love are never contradictory, they dismiss the idea of God's wrath in favor of an understanding of his love that is more in tune with human sentiment than divine sovereignty.
Another example is the nature of God, especially in terms of his being a "tri-unity", that is, one God existing of three persons. Too many times we find ourselves coming up with models of God intended to uncomplicated this very complicated and complex doctrine. Things like the egg, with its three parts, or water in its three states (vapor, liquid, and ice) only serve to introduce grave error into our minds. Better just to realize that all three persons of the Godhead are described, presented, and recognized in the Bible as having complete divinity while yet remaining distinct persons.
A last example here is the almost insufferable wrangling about the future. In the past century more speculation has been penned and preached about the timing and events surrounding the return of Jesus Christ than we are able to stand. It is interesting that the historic creeds and confessions contain almost none of these elements because they refused to go beyond what is clear in Scripture. We would do well to follow that example and put our intellectual energies into teaching the world what the Bible makes clear instead of wandering in the mists of speculative exegesis trying to find that final puzzle piece.
Third, while it is dangerous to go beyond the Bible, it is just as necessary to take into account all relevant biblical material when trying to determine what we are to believe. Understand this very carefully: Anything we hold to dogmatically must do justice to all applicable biblical material. Too often we get off track as a result of resting our case on one or two texts, while refusing to address the others that also speak to the issue.
For example, to understand "faith" properly we must not only take into account the many admonitions to "believe" also recognize that Ephesians 2:8 says faith is not something that originates in us but is a gift from God. Likewise, repentance is said to be God's gift in 2 Timothy 2:24-26.
Likewise, to reject the doctrine of God's sovereign election to salvation on the basis of 2 Peter 3:9 is to overlook both the actual context of that text, and the clear teaching of Acts 13:48 and Ephesians 1:4.
Ultimately however, it all comes down to trusting God in the dark, in those places where the light of Scripture just doesn't shine as brightly as we would want. We just aren't comfortable with mystery, with loose ends, with questions left unanswered. But, with age, it does get easier to restrain our curiosity, and leave the open questions to him.
For me, there is an increasing sense of appreciation for my God as I study and reflect on the truths he has revealed. And I have come to find great peace in trusting him to take care of all that remains hidden in the gaps between those things I can know for sure.