software transactional memory (stm) is a promising paradigm that facilitates programming for shared memory multiprocessors. in stm programs, synchronization of accesses to the shared memory locations is fully handled by stm library and does not require any intervention by programmers. while stm eases parallel programming, it results in run-time overhead which increases execution time of certain applications. in this thesis, we focus on overhead of stm and propose optimization techniques to enhance speed of stm applications. in particular, we focus on size of transaction, read-set, and write-set and show that execution time of applications significantly changes by varying these parameters. optimizing these parameters manually is a time consuming process and requires significant labor work. we exploit linear regression (lr) and propose an optimization technique that decides on these parameters automatically. we further enhance this technique by using decision tree. the decision tree improves accuracy of predictions by selecting appropriate lr model for a given transaction. we evaluate our optimization techniques using a set of benchmarks from stamp, nas and discopop benchmark suites. our experimental results reveal that lr and decision tree together are able to improve performance of stm programs up to 54.8%.