Like a child talking to a Father who already loves you, not like a performer earning a hearing. There's no required tone, no magic vocabulary, no quality bar your words must clear. He knows what you need before you ask. You can simply be honest.
The Grace Answer
A lot of us learned to pray as a performance. Choose the right words, strike the right tone, work up the right emotion, and maybe God will listen. So prayer became something we manage instead of something we rest in, and the quiet fear underneath it was that the quality of our praying determines whether God pays attention. That fear is exactly backwards.
Jesus addressed it head-on. “When you pray, do not use vain repetitions as the heathen do. For they think that they will be heard for their many words.” Then the reason: “your Father knows the things you have need of before you ask Him.” You are not informing God, and you are not persuading Him with volume or eloquence. He already knows, and He is already inclined toward you. Prayer is not a speech you deliver well enough to earn a response. It is a child talking to a Father who is already leaning in.
You can be honest
Because you have received “the Spirit of adoption by whom we cry out, Abba, Father,” you get to bring the real thing, not the polished version. Bring the anger, the confusion, the boredom, the doubt. The Psalms model this constantly, believers saying wildly honest things to God with no punishment for the honesty. You never have to assemble the acceptable version of yourself before you approach. The access was already secured by Christ, so you come as you actually are.
So how should you talk to God? Plainly. Honestly. In your own words or in no words at all. You do not have to sound spiritual, and you do not have to get it right. You are not standing before a critic grading your delivery. You are with a Father who already loves you, already knows, and was already there before you started to speak. And if all you can manage is a single honest sentence, or a sigh with no words at all, He fully knows your heart. The Father was never grading the prayer. He delights in the child who simply speaks to Him honestly.