Faith is a key, but you need not believe me. Test it. You need faith as big as a mustard seed. Doubt can lock the door. Experiment with faith. Use your faith muscles daily and build them.
Keep your body as healthy as possible with regular exercise and nutritious food.
Spend some time every day in some kind of quiet meditation or prayer. Seek first the Kingdom of God.
Renew your mind. If a doubt shows up, quietly and deliberately change your thought from doubt to faith.
Speak words of gratitude and faith. If words of doubt do come out of your mouth, quietly cancel that energy by speaking the word cancel out loud. Carefully craft all vibratory energy which you allow yourself to speak.
When you are around others, do your best to maintain a noble silence if negative conversations develop. Keep your mind on your gratitude for God's goodness in your life.
Get definite about what you want in your life. Consider the universal laws when making your choices, if what you want will harm others.
Follow Holy Spirit's guidance and do the work.