I think the problem of unity occurs mostly outside Iran, as Ahmad Betebi said to persiantoenglish.
We know that Iranians fighting for democracy have very different political views. In the same time, we know that unity is important in a struggle for freedom: we know very the meaning of "united we stand, divided we fall". But how? How can we get united? I try to write some suggestions:
1. the question of flag
Which flag do you prefer?
How important is that to you?
In some cities outside Iran, two groups didn't agree to demonstrate on the same time. Both of them chanted the same slogans against the policies of the Islamic Republic. Both of them wanted the freedom of all political prisoners. As one group was finished with the demonstration, the other group started! Why?
One group wanted to use the Iranian flag with the sign "Lion and Sun". The other group wanted to use a green flag. Both groups wanted the other group to use the flag of their own. What was the problem?
The second group said if they would use the flag with "Lion and Sun" symbol, monarchists would misuse them and say Iranians are wanting monarchy. "Green is the color of Iran protesters, so we use it". The first group said "Lion and Sun" was the national flag of Iran before the Islamic Republic, so every one has to fight under this flag. For sure there were also Iranians which demonstrated under both flags. There are lots of "green monarchists", and lots of greens who like the flag with "Lion and Sun"
1. The best solution would be to agree on one flag. If these groups are not able to agree on the flags of the others, they could agree on one anther flag, for example on "falcon standarad of Cyrus the Great".
falcon standard of Cyrus the great
2. Since they chant the same slogans, these groups can use their favorite flags but demonstrate together.
Libyans, despite the diversity of many tribes, showed that it is possible to fight united under one falg.
2. next system
We have to agree that the only solution for Iran's future, after the fall of Islamic Republic, is a free referendum. After a referendum we will see and accept what the majority of Iranians are wanting: a constitutional monarchy, a republic or something else. It is useful to talk about advantages and disadvantages of both systems. On the other hand, insulting each other doesn't help Iran's future. It just sickens any democratic atmosphere. Insulting is destructive for unity.
3. how we should behave towards extremists
We have to ignore extremists who cannot tolerate different oponions and distance ourselves from them. We have to make extremists clear that they are sickening the atmosphere in Internet. They have to know that we don't like people insulting other groups, although if they behave to be our supporters. We can e.g. unfollow and block them on Twitter and in Facebook. We have to ignore them till they understand their methods are not working in the 21st century.