Many databases index select protocols. You can generally locate them by including
(method OR protocol*)
in your search. Relevant databases are listed on the Research Articles tab.
You can also find books with protocols and methods by searching the library's catalog. Search "laboratory manuals" along with other keywords relevant to your search. For example, try:
"laboratory manuals" (biology OR microbiology)
Note: These sites are collections of protocols from multiple sources. Although, potentially very informative, remember that they have not all been peer-reviewed.