Are there any ways to reduce one's accent and speak with clear diction?

Yes. You have to practice. You have to know what you want to change and pay attention to what you are saying. Concentrate on saying the words the way you want to say them. It takes time and patience, and a lot of concentration. I have had to relearn how to pronounce a few words, and over the years it has gotten to be a habit to say the words correctly. Sometimes I try to mispronounce the words so that my kids can hear how I used to speak. They get a kick out of it. I grew up with a southern accent, but don't have it any longer, after years of working hard to loose it. There are a couple expressions that I still use (can't change everything), but for the most part, it is gone.