Some people are skeptical of scholars and commentaries in the same way I am skeptical of used car salesmen and contractors going door-to-door. The prejudice seems to run that these learned types are trying to take away our time-honored understandings of Scripture and baffle us with BS (that's Bible Study if you are easily offended). These well-meaning people fail to realize that any time they talk with someone else about the Bible, hear a sermon or a Sunday school lesson on a particular passage they are listening to commentary. Commentaries are merely a person's reflections on a book of the Bible. The best ones present sound exegetical proofs for their inferences and subsequent case for interpretation. Commentaries are conversation partners we invite into our dialogue.
Other Christians have the opposite problem. Rather than engage in a conversation with several informed voices, they read one or two commentaries and take everything they have to say as God's honest truth without doing any of their own study. No interpretation of Scripture outside of the Bible is inspired, so we can't afford to hand off our brain to another interpreter. So, what is the proper way to use commentaries in the service of Biblical interpretation? Read two or more only after you have conducted your own study.
My mentor, Dr. David Bauer, always teaches his students to inductively study the Bible, looking to such things as key terms and definitions, book survey, immediate and broader book context, word usage, NT and OT usage, etc. before they ever pick up a commentary. However, reading a few commentaries is an important part of interpretation because without other scholars weighing in on a subject it can be quite easy to see what you want to see in a particular passage. The scripture doesn't belong to you or me--it belongs to the Church, and it is in the community of faith that we should interpret it.
If you are new to reading commentaries and are not sure how to get started, you should know a few things. There are several types of commentaries aimed at different levels of learning. There are devotional commentaries, which illustrate the scholar's interpretation but offer few to no proofs along the way. These can be edifying (or even good for sermon helps) but they aren't helpful for a student engaged in deep study. You need to be able to understand how the commentator got there. Commentaries of this type would be Matthew Henry's Commentary or N.T. Wright's "New Testament For Everyone" series.
Then there are exegetical commentaries, which build a case for an interpretation from the text using such things as original languages, grammar, context, historical background, etc. There are numerous types of these with various levels of technicality. Some are easily read by a lay person while some are difficult for an academic. Personally, I use the IVP New Testament series, Tyndale New Testament series, Word Biblical Commentaries, New International Commentary on the New Testament (NICNT) and New International Commentary on the Old Testament (NICOT), and New International Greek Testament Commentary (NIGTC) to name a few. If you want further help in selecting good study resources, I highly recommend Dr. Bauer's An Annotated Guide to Resources For Ministry.
Please let me know if this has been helpful to you or if you have any thoughts or questions.