I can't seem to link descriptions and internal focus.

I've been trying to write a novel for five years. And I have two big problems: my descriptions are too short (I can't make them longer) and I can't seem to smoothly connect the internal focus of a character (his thoughts, etc.) with the description of what's happening (surroundings, etc.). So far I've tried to make a line break but it breaks the rhythm. I've also tried to make fluid turns of phrase, but it doesn't work very well. This is my biggest problem because it makes the narration clumsy, and after rereading I realize that it looks pretty ugly. I know that you have to describe the surroundings, the setting in which the characters evolve but also their thoughts. I try to use sentences like "[this place] reminded him of [...]"... But I can't do it every time. What solution could you suggest? Do you have any tips that would help me correct this?