I attribute to God everything that is consistent with the values and desires demonstrated by God through God's actions in the Bible, in the time since then, and in our modern time. Basically, does it bring people closer to God, to God's truth, love, and life? Does it bring people closer to eachother at the same time as well? Or does it tear them apart or allow them to remain distant? Does it allow them to 'honor God with their lips while their hearts are far from him' (matthew 15:8) or does it demonstrate the heart of passion and character we see in Christ?
There are various ways to recognize God's involvement -- the fruit of the spirit (galatians 5:22-23), the qualities of 'wisdom from above' (james 3:17), the description of Love (1 corinthians 13:4-7), the fruit of our actions (matthew 7:16) and our love for eachother (john 15:35) and even the description of wisdom (proverbs 8).
You decide what is or isn't from the Holy Spirit by knowing the Holy Spirit. Developing that relationship involves risk, like stepping out of a boat and walking on water. Ironically, walking by faith to know God, is safer than using scripture by itself, as a kind of boat. Peter was safer walking with Jesus on the water, than he was in a man-made boat which was otherwise at the mercy of storms.
That said, boats aren't bad -- Jesus used them and he built stuff for people to use too. But the things God gave us are not a replacement for direct reliance on God.