When I was getting ready to go through the temple for the first time, I was told maaaany many different things. I heard stories about missionaries that went once and would never ever go again because it freaked them out. I heard about people that said it was so weird that it made them doubt the church they'd been a part of their whole lives. Other people told me of magnificent experiences of the spirit. My stake president told me that the biggest defining factor that determines our first temple experience is our level of preparedness.
When he told me this, I started right away doing all I could to prepare myself to have a good first experience in the temple of my Heavenly Father.
I read a fantastic book (Thanks Grama!) called "The Holy Temple" by Boyd K. Packer. It helped me realize that the endowment is what gives us everything we need to pass from this life to the next. It is helpful for our life now... but mostly we are just practicing to enter into the presence of our Heavenly Father!
It also talked about, as a bajillion people told me before I went through, that the temple is like 99% symbolism. I know some people struggle with this... but it made perfect sense to me! In Christ's day, he taught in parables and symbols. One day His disciples said to him, "Can't you stop with the symbols and just tell us what we need to know?" (clearly not exact wording) :) The principle the Savior taught is that everyone is at a different place with their knowledge and understanding. By teaching with symbols, EVERYONE can learn no matter what stage of life and knowledge they are at. The temple is designed for us to learn for 80+ years. It is symbolic so you can learn on your first time... and you can learn on your 100th time.
It is really a beautiful day and a glorious session. If you are spiritually prepared then nothing will come as a shock to you. Pray to have the spirit with you that you may know of the truth of the ceremony and feel what you need to feel for your first time. Everything kind of just makes sense and feels right. It feels familiar.
Whilst pondering before I went through the temple, I thought about how some people think the temple is cultish after they go through because of the repetition and symbolism. I realized that every single ordinance we perform in the church contains two things: Symbolism, and repetition. Baptism is symbolic of the death and resurrection and the cleansing of our sins with the immersion of water and it is so important that we have a prayer repeated every time. The Sacrament is symbolic of the flesh and blood of Christ and is so important that we have a repeated prayer every time. Why would the ordinances performed in the temple be any different?? As my wise missionary best friend, Sister Leslie Dixon in Finland, told me, "If baptism were too sacred to talk about, people would think that being dunked under the water was strange and shocking. The only reason the temple is strange to people is that it is too sacred to talk about." But if we are spiritually prepared and have the spirit with us, there is nothing to fear! Everything will feel familiar and we will feel peace.
In my mission prep class we talked about how receiving our endowments should be MORE exciting than receiving our mission calls! You don't have to go on a mission to go to the Celestial Kingdom... but you DO have to go to the temple. It is the best place in the world and I am so grateful for the blessings I've received through the House of the Lord!