There have been some good answers here, particularly that of AJweb.
However, there is one other point, worth making about pronunciation. There is not one, particular way of pronouncing English. This is because of the big differences in the forms of English that are spoken around the world. They involve different accents, as well. Accents have a very big effect on pronunciation.
As with learning English generally, it is best to decide before you even start which form you want to learn. In terms of pronunciation, this means deciding if you want to learn a particular accent of the English-speaking world — or not.
If you do, you should look for resources that will expose you to it. For example, if you want to learn an American accent, look for American resources. Listen to American films and television programmes, or practice with Americans.
If you don't want to learn a particular accent, but want to pronounce British English neutrally, you should look for resources that will expose you to English English. That is, the pronunciation of English people without a particular regional accent. What is also called "British English". For example, listen to BBC radio, watch British television or, speak to British
Although there are plenty of regional, British accents they are generally not as different from each other as they are from non-British accents of the English-speaking world. This is of good quality, is neutral (without an accent), and can generally be understood around the world.
Decide who your audience will be.
If you mainly or only want to speak English to people who speak in a particular accent (for example, American English or Australian English), you can learn that accent. Even then, it is not always necessary.
If you mainly want to speak to English speakers generally (whichever form they speak), you don't have to learn an accent. You can learn neutral pronunciation, which will be sufficient.