It is well known that English favors language diversity. Thus, when you cite ideas from other papers, you should avoid overusing the word "say." For example, in the following paragraph, all the highlighted words simply mean "saying." However, if you replace these words with say, your essay sounds very dry.
There are many sources that teach you how to use reporting verbs. I personally recommend the one developed by The University of Adelaide, please click here to download.
ACCORDING TO
ACKNOWLEDGE
ADDRESS
ADVOCATE
AGREE
AIM
ALLOW
ANALYSE/ANALYZE
ARGUE
ASK
ASSERT
ASSUME
BELIEVE
BUILD
CALL FOR
CATEGORIZE/ISE
CLAIM
CLARIFY
COIN
COMBAT
COMMENT (ON)
COMPARE
CONCERN
CONCLUDE
CONDUCT
CONFOUND
CONSIDER
CONSTRUCT
CONSTRUE
CONTEXTUALISE/IZE
CONTRIBUTE
CULL
DECLARE
DECOMPOSE
DELIVER
DEMONSTRATE
DERIVE
DESCRIBE
DETAIL
DEVELOP
DISCUSS
DISTINGUISH
DOCUMENT
DOUBT
ECHO
ELIMINATE
EMPHASISE/IZE
ESTABLISH
ESTIMATE
EVALUATE
EXAMINE
EXEMPLIFY
EXPAND
EXPLAIN
EXPLORE
EXPOSE
EXPRESS
EXTEND
FIND/FOUND
FOCUS
GAVE
GENERATE
HIGHLIGHT
HYPOTHESISE/IZE
IDENTIFY
ILLUSTRATE
IMPLY
INDICATE
INTRODUCE
INVESTIGATE
LABEL
LAMENT
LOOK (AT)
MAKE USE OF/USE
MEASURE
MENTION
MODEL
NOTE
OBSERVE
OFFER
OUTLINE
POINT OUT
POSTULATE
PRESENT
PROMOTE
PROPOSE
PROVE
PROVIDE
QUALIFY
RECOMMEND
REEXAMINE
REINFORCE
RELATE
REMIND
REPORT
RESEMBLE
REVEAL
REVIEW
SAY/SAID
SEE
SHED LIGHT ON
SHOW
STATE
STUDY
SUGGEST
SUPPORT
SUSPECT
TACKLE
TAKE
TEST
THEORISE/IZE
URGE
VIEW
WRITE/WROTE