Here are some resources which may help you:
Macmillan Dictionary is a good dictionary for English learners as the definitions are written in a direct way and each entry has an audio clip so you can hear how the word is pronounced.
By learning the phonemic chart (a table of all the sounds used in English) you will also be able to read the phonemic script of any word which can be found in dictionary entries. I personally find that the Adrian Underhill phonemic chart is the most logical and easy to memorise. This interactive chart will help you study the sounds.
Cambridge English Online is a fun interactive website where you can practice English sounds through online games.
The Cambridge University Press interactive pronunciation resource not only teaches phonemic script but also intonation (the rise and fall of the voice in sentences and questions) and stress (emphasis given to syllables or words) with animated characters.
If you are looking for a study book then the Pronunciation in Use series by Cambridge University Press covers all the main aspects of pronunciation and books are accompanied by CDs. I often refer to these books when teaching pronunciation classes.
Of course, it’s also important to hear authentic examples of speech as this can help you understand different accents.
Due to the history the UK and the mixture of languages and dialects of it's indigenous people, there is a wider variety of accents here than any other English speaking country. There is no such thing as “a British accent”.
If you travel in the UK or do business with people from there, you will almost certainly encounter a range of accents.
The British Library has collected samples of many different British accents. In fact you can listen to 71 sound recordings and over 600 short audio clips.
Book a Skype lesson to practise your pronunciation with a native English teacher.