In 2 Nephi 9:39 there is a simple phrase that I learned to love and apply on my mission.
"To be Spiritually Minded Is Life Eternal."
If you notice, the first letters of each word spell SMILE.
I honestly believe that is what got me through every single trial I went through on my mission. I knew that the mission was going to be difficult, but I really could not have planned for or imagined the individual trials I would be given.
Your mission is specific to YOU, and so the trials you will be given will be your very own. The advice I would give is right out of that scripture in 2nd Nephi- Be spiritually minded, and don't forget to SMILE!
Being spiritually minded means to learn to focus on the eternal perspective and to forget about everything temporal. I found that when I focused on myself or anything besides the work, I was not happy.
Part of being spiritually minded is to remember the Savior during the hard times and recognize that what you are going through is tiny compared to the suffering He went through for each of us. When I am spiritually minded, I SMILE because I really feel blessed to have a knowledge of the gospel, and the privilege to give others the same knowledge.
I also found that by having a spiritual mindset and a smile on my face, people seemed to be much more receptive. A smile really makes all the difference in your life and has an impact on others. It essentially portrays what the gospel is to those who are unfamiliar with it.
I promise that if you can apply this scripture on your mission, you will be able to rise above the difficulties and challenges that will be presented!