Remember: Monera comprises archaebacteria and bacteria and Protista comprises protozoans and algae.
Differences
Monera: prokaryotes; Protista: eukaryotes. Monera: unicellular; algae (part of Protista): some pluricellular.
Similarities
Protozoans and bacteria: unicellular; part of the group is heterotroph (non-photosynthetic bacteria and archaebacteria, protozoans), the other part autotroph (photosynthetic bacteria and algae).