The main rule here is: Practice makes perfect. First of all, make sure you can easily complete exercises on the page Learn Russian alphabet: Lesson 2.
Plus, work more with Russian vocabulary, for example, on our website - Vocabulary section, where you can Russian words with translation and pronunciation. The more words you know, the better and faster you read.
Also, we recommend you to read Russian texts aloud, one text several times. You can find texts for reading here