Something that I often confuse while writing is the correct usage of that and which, even though there are some simple rules to determine which of them is appropriate.
A relative clause starting with that cannot be removed without altering the meaning of a sentence (restrictive/defining clause). In contrast, the pronoun which conveys some additional information (nonrestrictive/non-defining clause).
As clauses starting with while are not mandatory, they are always enclosed with commas.
- The bike that is broken is in the garage.
There may be several bikes and only the broken one is in the garage.
- The bike, which is broken, is in the garage.
There is only one bike and this bike is broken.
See here for some more examples
-  That vs. Which on dailywritingtips.com