Don't speak or write too early

If you follow the above rules and still make a lot of mistakes when speaking (= more than 1 mistake every 3 sentences), you should probably switch to writing for a while. Consider the following guidelines:
First write, then speak. Writing is easier than speaking because: 1) you don't need to have good pronunciation (but you need good spelling),
2) you can write very slowly and nobody will mind,
3) you can use dictionaries, the Web, etc. So, it's a good idea to practice writing first until you can build correct sentences quickly enough for speaking.

Don't speak until you've learned to pronounce English sounds. You need to be able to pronounce all the English vowels and consonants in a clear way before you speak. If you don't, you will get used to bad pronunciation.
Don't say a word if you don't know how to pronounce it. In other words, you need to know the pronunciation of all the words that you use. If you don't, you will be making pronunciation mistakes and teaching yourself bad habits.
If you make more than 1 mistake every 3 sentences when writing in the slow and careful way described above, you should probably stop writing for some time and concentrate on reading and listening.
Remember that you should first get lots of English sentences into your head, then build your own sentences. Your main activity should be reading and listening to English - and the reason is that you need good examples to follow before you can build your own sentences. The more sentences your brain absorbs, the more you can express in English. If you don't see/hear enough correct, natural English sentences, you will not know how to say things in English. So you will be inventing your own language. And you will be making mistakes.