Over the recent years, the study of language learning strategies has received much attention worldwide in general, and in Iran in particular. Many scholars have tried to investigate the function of language learning strategies in EFL learning and teaching. Not enough attention, however, has been paid to language skills, especially speaking skill, in Iran. Therefore, the present study aimed at shedding some light on language learning strategy and speaking, through answering the two research questions: 1. What Language Learning Strategies are used by successful language learners? 2. Does instructing Language Learning Strategies used by successful learners to less successful learners have any significant effect on developing their speaking ability? To collect information, Oxford's (1990) SILL, Naiman's (1978) GLL questionnaires, along with the two proficiency tests including TOEFL and IELTS were utilized. The results revealed that successful language learners use a variety of strategies; memory strategies being the most frequently used strategy, and metacognitive strategies being the least frequently used ones. T -test was used to test the hypotheses, and it was revealed that instructing learning strategies to less successful learners significantly affects their speaking ability.