-er is used for person, who does an acrivity (writer)
-or - sometimes the er suffix is written as or. It's worth making a special list of them as you meet them (actor)
-er/-or are also used for things which do a particular job (projector)
English Vocabulary in Use Upper-Intermediate, p23

-er and -ee can contrast with each other meaning

• -er - person who does something
• -ee - person, who receives or experiences the action

employer/employee, sender/addressee
English Vocabulary in Use Upper-Intermediate, p23

-(t)ion/-sion/-ion are used to form nouns from verbs (complication, promotion)
English Vocabulary in Use Upper-Intermediate, p23

-ist and -ism used for people's politics, beliefs, ideologies and (some time) profession (terrorist, journalism)

• -ist - a person
• -ism - an activity or ideology

-ist is also often used for people who plays musical instruments (pianist)
English Vocabulary in Use Upper-Intermediate, p23

-ness is used to make nouns from adjectives (goodness)
English Vocabulary in Use Upper-Intermediate, p23

-able/-ible with verbs means can be done (readable, flexible)
English Vocabulary in Use Upper-Intermediate, p23

-ise/-ize forms verbs from adjectives (modernise, industrialise)
English Vocabulary in Use Upper-Intermediate, p23

• -ment nouns (replacement)
• -ity nouns (flefibility)
• -hood abstract nouns especially family terms (childhood)
• -ship abstract nouns especially status (friendship)
• -ive adjectives (passive)
• -al adjectives (legal)
• -ous adjectives (furious)
• -ful adjectives (hoppeful)
• -less adjectives (useless)
• -ify verbs (terrify)

English Vocabulary in Use Upper-Intermediate, p23

Vocabulary Rules