I think it boils down to where your special help would be useful. If you pass a car accident, yes, your physical presence means you have a unique ability to help.
Likewise, when it comes to personal interactions, people are not interchangeable. Getting a card or letter from a stranger is not so comforting as hearing from someone you love. We evolved to interact with people we know in real life, and this still satisfies us more than some abstract kindness from a stranger.
So recognize the areas where you can be uniquely helpful: being kind with your family and friends. Sudden emergencies where you are physically present. Being a good neighbor.
But here's where I think people go askew with this logic: they feel that financial help should also work this way. After all, don't I understand the needs in my own community better than anyone? So I should fund projects in my own community, and other people should take care of theirs.
But rich people live in communities with other rich people, and poor people live near poor people. Your average American probably has several relatives or neighbors who have a few thousand dollars in their bank accounts. Your average Nigerian does not know any such people. When both rich and poor people give within their own communities, the opera gets a lot more funding than the maternal health clinic in Nigeria.
Of course, lots of first-worlders have given misguided aid because they misunderstood the needs of people in other countries. But you can misunderstand the needs even in your own community.
Last summer when I was studying in Ecuador, several of my fellow travellers volunteered in a local orphanage. The place was in bad shape, and it was hard to see the kids living in deprivation without wanting to do something. So some Americans decided to raise money for the orphanage from their friends at home. After all, they saw these kids every day and had seen the need first-hand.
Except they found out the reason the place was falling to pieces was that the owner was embezzling money. Those donations would probably never have reached the kids. Americans weren't alone in being duped by this guy. Every Christmas he had a big fundraiser and lots of Ecuadorans gave money, clothes, and toys. The locals were just as misinformed, despite it being in their own community, because they hadn't seen the financials.
This can happen in any country. At home in the US, I saw a lot of misguided community help during the summer I worked in a domestic violence shelter. We had a garage overflowing with blankets, because people had this idea that battered women need blankets. What they actually needed was a child's car seat so the children could safely ride to doctors' visits. The fact that donors were local didn't give them special insider knowledge about the residents' needs. It would have been better for them to donate cash so that we could use it for what was most needed (the car seat, not more blankets).
There are good and bad charities working in all parts of the world. Find ones that will use your money well, and that are doing important work. (And if you live in a rich part of the world, the greatest need probably isn't local.) Then donate money, which will help more than your blankets, old clothes, or volunteering.
And then find someone you love and give them the hug or the kind word that only you can give.