The Holy Spirit is the kind of person who is by your side and who you would want by your side. It is, perhaps, a legal implication as one who is called to represent us in court. The primary way is through the illumination of the Bible. Other ways include the teaching of others and through circumstances. Impressions are often thought of as the primary way the Holy Spirit teach us.
Impressions are, in fact, the least reliable way.
Impressions are impressions. Sometimes they are the Holy Spirt and should not be ignored. Sometimes they are not and can be safely ignored. One of the great things groups can do for one another is to give to each other confidence from sharing with one another how God has been good to them. When Jesus was here on earth, he was limited geographically.