The Carnegie Hall method: Practice, practice, practice.
You were able to come up with the cooked noodles metaphor, right? So clearly your describing skills are not broken. You just have to work them out.
Get a notebook. Moleskine, marbled-cover, stack of pages stapled together, whatever works.
Set aside time every day — start with 15 minutes and work up. This is your practice time.
During this practice time, pick something to describe. It can be an object, a sensation, the weather, sunset, a person, the dog, a texture — something you can observe in some fashion. Try to keep it concrete and literal at this stage.
Write down your descriptions. They can be prosaic at first (grass is green), but you must work the whole 15 minutes. After you've stated that grass is green, you have to come up with something else to say about it. What does it smell like? Is it sharp? smooth? is the tip pointed or chopped off? Are there other kinds of grass next to it? Is it a pure green or bluish or brownish?
This forces you to a) really look at something b) put your observations into actual words c) write those words down.
There's a similar question on this Stack about describing pain which you might find useful: Effective techniques for describing pain
Eventually you will go beyond "grass is green" and start coming up with figures of speech just to have something to say to fill the 15 minutes. The more you do this, the easier it will become.
Once you've gotten better at Things You Can Observe, start practicing with Things You Can Remember. Write down everything you recall about a particular moment in time.
When you feel comfortable with transcribing your memories, you can start practicing with Things You Can Imagine. And that's when "legs like cooked noodles" will start to pop up.