Filters are verbs you might be using to tell us what your character is thinking or perceiving. Here’s an example:

Wendy realised that she had forgotten her lipstick.

This should be replaced with something like:

Wendy sat herself in front of Bob’s mirror and dipped her fingers into her purse.
“Oh shit, I forgot my lipstick.”

Another example:

Telling: Lisa heard Mike laughing.
Showing: Mike laughed.

These are the words that might be weakening your story:
see, hear, think, wonder, realise, watch, look, seem, feel, can, decide, sound.

Using the above words is another way of telling instead of showing. Something we try to avoid when writing.