With regards to various social movements, an ally is an individual who is not part of the group that directly benefits from that movement but still wishes to fight for that cause. A good example of this, which will be used throughout this article, is a heterosexual individual fighting for homosexual rights.
To be an ally of any movement is to put yourself in a very interesting position. You must be aware of your motivation to act as an ally, especially when you are not affected in any way by the cause you are fighting for. You must be aware that no matter how much good you do, there will be people in your cause who will not accept you. Most importantly, you must constantly be aware that you never get in the way of your cause and let your ego come first.
A person can have many reasons for becoming an ally. For example, a straight ally might have gay family or friends and wish to see their lives improved. However, when the ally is not at all affected by their cause, they must examine their reasons for being an ally carefully. Do they wish to see lives bettered, or to see a better future? Or are they doing this to rebel against the system, their parents, etc.? Are they acting as an ally to put on an image for others, or to puff up their ego ("Look what I'm doing!")? If any of these are the case, then the ally is not truly an ally, as they are only using that particular cause for their own ends. The ends of that movement are not their own.
An unfortunate truth of being an ally is that you are an outsider. You can heavily empathize with your cause, but it is very likely that you will never experience what the individuals in that movement go through: a heterosexual individual is not going to have to deal with homophobia. Due to this outsider status, there is a good possibility that there will be individuals who will never 100% accept you. The unfortunate truth is, you'll be viewed as a downright enemy by some. The only thing to do here is to not get discouraged and keep moving forward. The lack of acceptance will be heavily overshadowed by those that do accept you and are happy for the help.
The most important part about being an ally, however, is never letting yourself get in the way of the cause. There are far, far too many "allies" who are only in it to make themselves look good: it's an ego trip. It's more about the selfies they can squeeze in than any good that they can accomplish. Other times, it is not outright maliciousness but ignorance that trip up the aspiring ally. If an ally is not properly informed about what is factual or what is and is not acceptable to that movement, they can do more harm than good.
The most important thing that any ally of any movement can do is listen . Do not assume you know more or even as much as those who do struggle on a daily basis. If someone calls you out on problematic behavior, you accept the criticism and learn from it. You may be joining the fight, but it is still their war.
If you ever find yourself in a position where you can be an ally to a movement, take it. People might listen to you where they will not listen to your movement. An ally has a very important responsibility, and with it, they can help change the world.