The process can seem overwhelming. There are so many areas that need improvement. Teshuvah does not mean trying to change everything at once. It is the beginning of a process that allows us to realistically change our behavior.
One suggestion for doing teshuvah effectively is to pick one small area and make a concerted effort to change it. The smaller the behavior the easier it is to change.
Rabbi Volbe Shlita presents the following mashal (parable) in the Alei Shur. If a plane flies too high in an air combat zone, it will be spotted on enemy radar and shot down. The key to survival is flying below the radar. Similarly, if we try to change too much, we are likely to fail. If we only take small steps to improve, our Yetzer Hara (Evil Inclination)'s radar will not think it is in danger and will not bother giving us a problem.
There are forty days between Elul through Yom Kippur. Forty days is very significant in Judaism. According to Chazal it takes forty days to form a fetus, the flood lasted forty days, and Moses got the Torah after being on Sinai forty days and nights because it takes forty days for a person to transform him/herself into a new being.
Between the forty days of Elul and Yom Kippur, take one small deed and try to improve. It can be saying a brocha (blessing) with added kavannah (concentration), saying a kinder good morning to a spouse, or not speaking Lashon Hara (negative comments about an individual, family or institution) ) for fifteen minutes a day. Whatever it is, that small step can make the difference.