Clue repeated patterns (diagrams/trigrams) in the ciphertext, which often indicate repeated words like "THE", and using the Kasiski examination or Index of Coincidence to determine the keyword length
donttrustmebuttru clue for solution after solve
The sun is important. The brightness impacts the day but the brightness might be a clue a little light is not bad The brightness helps with pictures to help us light the day light is important, but are you important too