At what level of detail does God lead His children? It seems that some people worry and pray about every aspect of their life, while others only sweat the big stuff. For example, I doubt any believer does not pray about whether they should marry a certain person or not. But for less significant matters, some pray about what God's will is and others just make a decision without prayer.

Should you pray about what career you should choose? About what book you should buy? At what point should you just make a decision?

Does the Bible indicate an answer to this question?

Note: I found a similar question here.
I would argue that ideally the Christian life would be fully marked by the leading of the Spirit.  (Don't get too nervous about this - God isn't a taskmaster - His will is not oppressive, contrary to popular belief.)  Here is the Biblical basis for this argument:

The first is a statement from Jesus, our perfect example, our Rabbi of which we are to be disciples and immitators:


  “I can do nothing on My own initiative. As I hear, I judge; and My judgment is just, because I do not seek My own will, but the will of Him who sent Me." -John 5:30


To clarify our calling as Christians, here is Paul's post-ascension teaching on the matter:


  and He died for all, so that they who live might no longer live for themselves, but for Him who died and rose again on their behalf. -2 Corinthians 5:15


In contrast, one of the sins which condemned Saul was not inquiring of the Lord:


  So Saul died for his trespass which he committed against the Lord, because of the word of the Lord which he did not keep; and also because he asked counsel of a medium, making inquiry of it, and did not inquire of the Lord. Therefore He killed him and turned the kingdom to David the son of Jesse. -1 Chronicles 10:13-14


There are many other passages, but this should suffice.  Our mindset needs to be: 100% devotion to the leading of the Spirit, 0% devotion to living for our own purposes.

Now, practically speaking, there are times to rest, times to fellowship, times to have a drink, times to read, times to gaze at the stars, and so on.

At what point should you just make a decision?  Well, technically, at every point.  Everything you do, whether "led by the Spirit" or "led by your flesh" is technically "a decision", so in every case you should "just make a decision" -- with the understanding that in every case you should "be sensitive to the leading of the Spirit", if He is leading, and in every case you should "guard against the lusts of the flesh".