You can understand english, that means you have 50% perfection in english. You just want to improve another 50% part of english that is communication skills. If you want to speak english, you have to speak english. If you make mistakes while speaking, doesn't matter, you always try to speak english. For speaking english you have to improve your grammer & vocabulary knowledge, read english newspaper daily, listen english newschannels, watch english movies, find atleast one partner to with you will speak english. Always think in english, it will definately help you to improve your speaking in english. have a nice day, by.