How does Bram Stoker provide in the text of "Dracula" ways in which people can overcome becoming evil?
I completely agree that being united and that emphasizing solidarity are lessons we can learn from Dracula.
Although Stoker is inverting the traditional Christian "I offer you this blood as a symbol of my sacrifice" with his blood sucking monsters, he gives us the tools to ward off the "creatures of the night" and protect us as we journey through the world and into the heart of darkness. The first is Christian Charity (please note that although I specifically mention Christian, I am convinced that every good religion espouses "charity"). While Harker waits for the coach that will carry him hence, he is begged by the caring old woman not to travel. She frets and urges him not to go since it is the eve of St. George's Day. Christian charity is fully evident here as the old woman tries to help a complete stranger and demonstrates love for her fellow man. The allusion to St. George, i.e. hagiography, is another way we can shore ourselves against the tide of evil.
We can also resort to the use and study of Christian iconography since the old woman gives Harker a cruxifix to help him ward off evil. By using such religious symbols Stoker provides the reader with another way we can ward off evil, protect us from evil, and even bring us back from a shadowy existence if we fall prey to it.
There are many other examples of things we can do to ward off evil in the novel. We've given you a start.
One primary way is by relying upon others. By keeping a united front, the characters manage (at least for awhile) to ward off evil. There is virtue and strength in solidarity, for a person's weakness can be compensated for by the vigilence and attentive care of others. The traditional role of the male as the protective agent and the female as the vulnerable subject (remember the historical context!) cannot escape our attention.
In this light, note that Dracula is constructed around a series of exchanged letters rather than being presented in the usual narrative way. The importance of solidarity and trust are highlighted even more by using this epistolary form.