Adding:

rails g migration AddFIELDNAMEToMODELENAME FIELDNAME:TYPE

For example:

rails g migration AddNameToUser name:string

Removing:

rails g migration RemoveFIELDNAMEFromMODELENAME FIELDNAME:TYPE

Renaming:

rails g migration RenameColumnName

then in db/migrate/xxxxxxxxxxxxxx_rename_column_name.rb, add:

rename_column :table, :old_column, :new_column

And of course:

rake db:migrate