If all charities were as good as each other, then giving to less effective charities wouldn’t be a big deal. But there are huge differences. Just as we might shop around to find the best value car so we can shop around to find the best charities.
Tip 1: Visit GiveWell
http://givewell.org is like a price comparison site for charities. It has excellent in-depth analysis of the best charities and causes in the world.
Tip 2: Distinguish good charities from very good charities
A cataract operation can cure someone of blindness for about $35  . The same person can be provided with a guide dog for $50,000. There are charities doing each. Both charities are definitely helping people and doing good. But one is helping a lot more people with the same resources. There’s something awkward here. It feels nicer to give a bit to all the good charities. But in a world with scarce resources, that’s a very costly attitude to have.
Tip 3: Take a big step back
We all support causes close to our heart. Yet the causes close to our heart are the ones most visible to us and theses may not be the best places to give. What would happen if instead of saying: “my mother died of cancer, so I will support cancer charities” people said: “my mother died of cancer, so I will support the charities that save the lives of as many mothers as possible”?
Take some time to work out what you really want. Is the cause you are supporting important to you in and of itself or do you really want to save lives or prevent suffering or end poverty?
Taking a step back and broadening your options is the first step to making sure your charitable donations go as far as possible.
Tip 4: Evaluating a charity yourself
The charity evaluators like GiveWell.org are not the be all or end all of charity comparison, but they have put in thousands of person hours into charity research. If I was to donate to a charity other than the ones GiveWell recommend I’d want a good reason for believing that my decision was better than their research. A good place to start for evaluating a charity yourself is at: http://www.givewell.org/charity-evaluation-questions.
Tip 5: Other useful resources
There is also www.animalcharityevaluators.org which evaluates the best charities for reducing animal suffering.
Tip 6: Ask for help
If you have any questions then post in the comments below or elsewhere on this forum or on the effective altruism Facebook page.
(Acknowledgements: This post is not all my own work. I wrote this a while ago for a private audience and lifted text out of blog posts by Catriona M at http://closetomyhead.com/2012/04/15/why-closetomyhead/ and by Seb F at https://80000hours.org/2012/09/is-there-such-thing-as-a-bad-charity/)
 GiveWell review of Aravind “In 2007-08, Aravind performed a total of 285,745 surgeries, 200,123 of which were for cataracts.17 At a total cost of $10.1m, this yields $35 per surgery performed.” http://www.givewell.org/international/charities/Aravind