One of the most daunting things about learning Mandarin (aside from the characters) are definitely the tones. Native speakers of western languages and other tone-free languages have a hard time trying to imitate the tones: this might work if you just say a word or two alone and need to be sure you can be understood, but in saying a whole sentence, unless you want to speak like a robot, it won't work. Over the last two years, speaking with some Chinese teachers, I found out that the best way is simply to listen and imitate your teacher naturally, without thinking "hey, I have to say the third tone, then the fourth and then the second", this way it'd be more difficult, but if you just repeat after your teacher it'll become a lot easier. Think about it: if you ask a native speaker who is not accustomed teaching Chinese which tone are in a word, they'll have to think it over a bit, they, as native speakers, have just been accustomed at repeating after their parents, not at thinking about which tone they have to say. Even Chinese teachers sometimes have to think which tone they are saying: they know it, of course, but the fact that they have to think about it even for a second will tell you many things about this process. It's like walking: you don't say "now I put the right foot ahead first and then the left one" you just walk. At first it'll be difficult, of course, but with training, you'll start speaking with the right tones without even realizing it, that's what many advanced Mandarin learners will tell you.