Help With Plaits!

Please help! I`ve had long hair for years although it has been cut short too, and I much prefer it long. It`s also straight and I know that if my friends plait it and I leave it overnight it`s nice and curly the next day. But I tried doing it myself earlier with a plait either side (can`t do one at the back), and one side came out crimped and the other still straight! Has anyone got any tips for plaiting long thick hair so it doesn`t look a complete shambles?!