We've already philosophized about this topic, but Hillel Halkin puts it very, very well:
Being pro-Israel does not mean you have to support any particular Israeli government or its policies. You can oppose all of the policies of the Netanyahu government and still be pro-Israel. But I would list a number of things that you must also be.
First, you must understand why Israel is important. Israel is unique in human history, whatever its faults may be. And if you’re Jewish, you must understand that, no matter where you’re living, Israel is your country. You can be critical of its policies, but you must understand that they are the policies of a government chosen democratically by your own people. Second, being pro-Israel means having an empathic understanding of Israel’s problems. This means not blindly superimposing liberal American standards of what’s right and wrong without asking whether they fit the Israeli situation. Third, you have to understand that the threat to Israel’s existence is real. Hundreds of millions of people, most of them Arabs and Muslims, would gladly see Israel destroyed. Whatever mistakes Israel makes, has made, and will make, it’s always facing the danger of annihilation. Fourth, you cannot be pro-Israel today without understanding that Israel has become the focus of a worldwide revival of anti-Semitic agitation, and the Israeli-Palestinian conflict has been viciously exploited for anti-Semitic purposes. When you criticize Israel, you have to be careful not to do it in terms that may be usurped by forces that hate not only Israel, but all Jews—which includes you, Israel’s Jewish critic. American Jews have to ask themselves whether it’s helpful in any given situation to join the majority of world opinion against Israel. Suppose your criticisms lead to harmfully isolating Israel even further. You can’t be pro-Israel unless you seriously reflect on what taking responsibility for running such a risk means.
Hillel Halkin is a translator, political commentator and author of the bestseller Letters to an American-Jewish Friend: A Zionist’s Polemic.