"Good teachers and friends" means that two people are both teachers and students, friends and partners, and they are also good teachers and friends of each other. They learn and grow together, support and encourage each other and make progress together.
"A ray of light is getting better and better" means that when two people are together, their wisdom and strength, like a tiny ray of light, gradually become better and stronger. They illuminate each other's way forward, support and encourage each other even in difficult times, and face challenges together.
Generally speaking, this sentence vividly depicts the relationship between two people learning from each other, growing up from each other, supporting each other and encouraging each other, and expresses their gratitude to each other.