Write sentences first, check each one by yourself after writing. Once you found any mistake, correct it....then eventually start with long sentences and ....just keep practicing.

The best advice I heard for this is to listen to much audio and current media/music/tv/radio etc. The more you improve your general familiarity with how the language is spoken the more the tenses will make sense. Perhaps this advice is not for everyone but it helped me. There are many rules regarding tenses but the more proficient you are in the language you are learning the more natural it will come.