It is so great that you recognize the need to put God first. It takes so many people way too long to come to that point.
The biggest and most important thing you can do is spend time with God. Make spending time with God a part of your everyday schedule. Make it a priority. Be consistent.
So what do you do during that time? If you ask this question to a hundred Christians you might get a hundred answers because there is no right or wrong. However, there are some things that really help me that I'll share with you.
First, it's really important to spend some time in praise and worship. When you do this it literally opens the door to God's house. Find some wonderful Christian music. Sing along and really mean the words you're singing. You'll find it puts you in a real state of mind to talk to God.
Second, read the Word. There are lots of ways to read the Word. You can use a study guide like you'll find on this site, or you can just start reading. Learn about God's character. See what He has to say about how to live your life.
Third, pray the Word over your life. Both you and God know the areas of your life that need some help. Ask God to show you what to work on first. And then look up that area in the Word. Find Bible verses that talk about it. Memorize them so you can pray them over your life.
As you start this process you'll find that God is showing you things and telling you things you never saw or heard before. You'll become sensitive to the leading of the Holy Spirit. You'll find that certain things you once did you'll no longer want to do because they are inappropriate or unnecessary.
Pretty soon you'll want to be a blessing to the people around you. You'll want to spend time with your family that is filled with positive, uplifting stuff. It all starts when you take the time to get to know God.
But just know it's a journey. God will always be talking to you or showing you something new to work on. We'll never be perfect and we'll never arrive. We just keep working with God, asking for forgiveness along the way, and living the life God gave us.