When I can say these words by themselves I want to start trying to use them in some short phrases so that I can use my new correct pronunciation easily and fluently  in everyday speech.

by themselves 用在名词 words 后，作 words 的定语，意为 “这些单词本身”，用来强调被修饰词。跟主语 I 无关。例如：

Nature by itself, he writes, runs on "principles of balance and holism." 

自然界本身，他写道，是按照“平衡和整体的原则”运转的。

《柯林斯英汉双解大词典》

Risk by itself will not threaten the success of a project if it is recognized and addressed in a timely fashion. 

如果风险自身被公认为一种适时的方式的话，那么它将不会对项目的成功构成威胁。