Besides, 6th and 7th lines are too long for a poem.
Whoa! Lines too long for a poem? Ha :) That's the first time I've ever heard someone say that, no offense. :]
In my opinion, if the lines fit with the rhythm and flows smoothly (Although I'm not a poet, to me, a good poem has rhythm and flow - that's why I don't really like Whitman :), then it works, regardless of its length. But right now, I have to agree with Azeri. You could develop your lyricalness. Imagine that you are actually there at the beach, and imagine that you are describing it to a person who has never seen a beach before. Describe it so well that the reader himself can imagine that he is there with you at the beach. Make it sound like you are singing, so be sure to keep the flow and rhythm in mind.
btw, I don't want any rhyme.
Aww... I like poems that rhyme. :)
what should I write next?
That's for you to decide. Think of every, single possible minute details of the beach, write them down, and arrange them into your poem. That could give you a good start :]
And, most importantly:
What is your goal? What you want to say by simply describing beaches? I see only beautiful words joined togehter, but as a reader, I would like to sense something unique that belongs to you, that demonstrates your attitude. Everything that you wrote is quite obvious and does not require broad imagination or deep thinking to understand. I don't know if I managed to convey my thoughts, but this is what I got from your poem.
Every poem has a "thesis," even if it is as simple as "life is beautiful." From this poem, what overall message do you want to convey? If you are simply describing the beach, without certain reason, then this poem is not a poem, but as Azeri said, descriptive verse.
I have one suggestion though. You could take out "When I think of the beach" and simply start describing the beach. It will sound more lyrical and the reader will know, if you add more specific descriptions, that you are referring to the beach. :]