All sentences usually boil down to who did what. [subject] [does verb] e.g. He ate.
So start there, whether reading or writing.
After that you can step by step add on the details of where it happened (location), when it happened (time), to whom did it happen (object).
Those nouns usually are [some details describing the noun]+[noun]. e.g. yellow banana.
At first, ignore the details describing the nouns, until you have the basic structure of the sentence.
e.g. He ate in the kitchen. He ate in the kitchen at noon. He ate the banana in the kitchen at noon.
Then worry about the details.
e.g. He ate the yellow banana in the dirty kitchen at noon.
An additional tip, that I don't personally use, but many say works for them is they read a Japanese sentence from the back to the front (It basically facilitates this process).
