What did Epicurus say about ambition, or about the desire to improve oneself?

The major textual references advise Epicureans not to pursue politics, riches, fame, or other activities that are essentially competitive in nature, or require obedience or cooperation from other people. The common thread of this advice is that you cannot be happy if you are going to depend on other people to provide your happiness, so it is not wise to pursue happiness by seeking to "excel" over other people in any competitive endeavor.

But there is another sense of "excelling" that most people also associate with the word, and that is the important sense of not passively "accepting one’s lot in life," and working hard to succeed in taking advantage of those natural and proper pleasures that are within your power to achieve without violating some rule of nature. Phrases such as "accepting one’s lot in life" connotes idea that are fatalistic, religious, (and predominantly Stoic) and go against every central theme of Epicureanism, which is the pursuit of happiness through (1) the study of Nature and (2) action based on the results of that study.

For a few of the significant references to this issue, see the following:

PD 5. It is impossible to live a pleasant life without living wisely and honorably and justly, and it is impossible to live wisely and honorably and justly without living pleasantly. Whenever any one of these is lacking, when, for instance, the man is not able to live wisely, though he lives honorably and justly, it is impossible for him to live a pleasant life. <<<< One CANNOT live happily unless one diligently pursues wisdom, honor, and justice.

VS 5. We place a high value on our characters as if they were our own possessions whether or not we are virtuous and praised by other men. So, too, we must regard the characters of those around us if they are our friends. <<< It DOES matter what we think of ourselves, and what others think of us.

PD 29. Of our desires some are natural and necessary, others are natural but not necessary; and others are neither natural nor necessary, but are due to groundless opinion. << And thus we diligently pursue those that are natural and necessary, and we judge and act wisely in pursuit of those that are only natural (but we do not ignore them).

VS 33. The cry of the flesh is not to be hungry, thirsty, or cold; for he who is free of these and is confident of remain so might vie even with Zeus for happiness. << And thus we pursue diligently the goal of avoiding hunger, thirst, and cold.

VS 36. Epicurus’s life when compared to that of other men with respect to gentleness and self-sufficiency might be thought a mere legend. << Epicurus EXCELLED in gentleness and self-sufficiency.

VS 41. At one and the same time we must philosophize, laugh, and manage our household and other business, while never ceasing to proclaim the words of true philosophy. << We do NOT ignore or deprecate the value of the management of our household business.

VS 45. The study of nature does not create men who are fond of boasting and chattering or who show off the culture that impresses the many, but rather men who are strong and self-sufficient, and who take pride in their own personal qualities not in those that depend on external circumstances. << This one is VERY clear. We are to excel in our strength, our self-sufficiency, and our personal qualities that do not depend upon others.

VS 58. We must free ourselves from the prison of public education and politics. << This is very close to the key issue, for it is freedom from these that we require in order to secure our own happiness.

And for a reference that me be the most direct of all on this point:

VS 63. There is also a limit in simple living, and he who fails to understand this falls into an error as great as that of the man who gives way to extravagance.

Discussion about this question is here.