Often I will open up the manpage for a command already knowing the option I am searching for and read its description. Sometimes simply searching for the option works immediately, sometimes the option is referenced elsewhere, sometimes the option just appears as a substring in the preceding text.
As a concrete example, on my computer, right now, this is the sequence of commands to get to the -l option of ls:
man ls
/-l
nnnnnnn
In this particular case there is only one group of options and they are alphabetically sorted, so I could just scroll down and find the option, or do as above. In other cases not so much. Regardless, I would like to go directly to the line.
If your pager is less, which it often is, it supports regular expression search. For your example this works:
man ls
/^ *-l\b
Which anchors the match to lines starting with arbitrary whitespace followed by -l and a word-boundary \b.