In the first line Wordsworth uses personification and simile: 'I wandered lonely as a cloud'. A cloud can obviously not wander or feel lonely - these are human attributes or actions. The comparison effectively reflects the Romantic ideal of finding expression for the human condition in nature and establishes the link between man and nature. Furthermore, the line also expresses the idea of the poet or artist finding inspiration when he/she is isolated from the rest of mankind and is at one with nature - another Romanticist aspiration.
'Crowd' (line 3) and 'fluttering and dancing' (line 5) extend the personification. A large number of the daffodils seem to be dancing, celebrating their freedom and being in nature (natural).
The infinite beauty of the flowers and their link with what is natural is emphasized in the second stanza through the simile: 'Continuous as the stars that shine and twinkle on the milky way'. 'Tossing their heads in sprightly dance' is once again, personification, again emphasising the joy of nature.
Stanza three further extends the personification with the waves also dancing, but the daffodils joyously outdances them. Wordsworth says that their company is 'jocund' - they are full of joy and life. The metaphor emphasizes the joy nature can bring, for the speaker declares that he 'little thought what wealth the show to me had brought'. He was enriched by the experience without even realising it at the time.
The value of the experience lies within the speaker's memory. So charmed was he by witnessing these beautiful daffodils that 'my heart with pleasure fills and dances with the daffodils', whenever he is in deep thought and recalls the experience.