Yes, that's true (I agree with Nacir's statement). By just learning the ready-made sentences (in a phrase book or audio materials) we can speak without thinking how to make sentences. Learn by heart, think about how the sounds affect our feelings, and abandon the visual form of the script. More effectively, learn in phrases. We can call this as a phrase module. There are noun phrases, verb phrases (such as modal verbs, phrasal verbs), prepositional phrases, basic clauses (subject and verb), adverbial clauses  etc which are frequently-used phrases. Just combine these phrases in line with what we intend to say. This is better than thinking in word by word. So, there is not so much grammar to be occupied with.

Simon, I think the key is "listen" and "practice". First of all, learn by heart standard ready made sentences, so that when you speak these you don't have to think and translate in your mind. For example, "tomorrow, it will be too late". If you have learnt that by heart without bothering about the grammar, you will always say the correct sentence. Listen to radio, news, talk shows, documentries, films, songs and listen a lot until you understand what they say. And with time you will be able to make sentences of your own with less effort. 

I agree with Nacir's statement; listen carefully and immitate the pronunciation and accent. To make it easier just put it in syllabic chunking. Imagine the sound of a syllable which consists of a consonant sound and a vowel sound. There are three kinds of basic syllables; consonant + vowel (CV), vowel + consonent (VC) and consonant + vowel + consonant (CVC). The extended are such as CCV and VCC. This applies only in English. Other languages have more complex such as CCCV and CCCCV in Slavic languages. Practise the syllabic sound to get the taste of the pronunciation and accent. 

I totaly agree with Nacir, Before 6 months ago I couldn't be able to speak one sentence but now I can speak English since I started to listen alot to English records. Surely, I am not good enough but I am doing great in no time :)

Thank you you guys for concerning the topic and sharing your valuble experences. all of you are kind-hearted.

How can we think of sth. in English directly? how to develop this sort of English thought?

When I try to speak English, somehow, i can't help to translate the sentences in my head, which result in the delay of speaking. and then the person you are talking with would be impatient, which impact on the effciency of speaking. and i think this is the common problem of Chinese students...