There are many differences between Spanish and English pronunciation. English is a time stressed language, as opposed to Spanish , which is a syllabic language.
This is important because we, as Spanish, try to give equal importance to each syllable but in English, only some words in a sentence are considered important and therefore pronounced with more emphasis (Content words) while others are quickly spoken (Function words) some would say ,swallowed.
Look at these two sentences. Although the first has 7 words and the second 12 , it should take you the same amount of time to read both sentences. Why? Because as English is a time stressed language there is always the same distance between two stressed words.
Peter said horrible things about your mother.
He left after dinner taking most of his books in his suitcase
Another thing to take into consideration is Linking .Words , when they are pronounced in isolation do not sound the same as when pronounced in a sentence. Why? Because of this linking.
Linking occurs in English in these situations:
Consonant+ vowel : when a word ends with a consonant sound and the next one starts with a vowel sound , we , very often , link them
Ex: Liked it /laiktit/
       And I /∂nai/
Vowel+ Vowel : when one word ends with a vowel sound and the next word begins with a vowel sound, we link the words with a sort of W or Y sound.
To simplify :
♥ If our lips are round at the end of the first word, we insert a W sound:
        Ex: do it /du:wit/
♥ If our lips are wide at the end of the first word, we insert a
Y sound:
       Ex: Ray is /reiyiz/
And then we have the Linking "r" for example, the "r" in "here" would not be pronounced in "Here they are " (because it is followed by a consonant), but it would be pronounced in "Here I am". Likewise, the "r" at the end of "far" would only be pronounced if the next word begins with a vowel, as in "far away" /fa:r∂wei/ or" far off". /fa:rof/

Listen to these sentences and repeat after them paying attention to the linkings
 Not at all
Isn't it a pity Ian's wearing odd socks?
Was ever a bride so pretty?

Here is a  song to practise linking. Pay special attention to the chorus where linkings are much more noticeable.  If you want to to an exercise with this song click here.