A recurring feature at IsraellyCool is a guide to hasbara featuring a different mistake pro-Israel advocates make each Tuesday. In that vein, I would like to suggest my own principle for how to advocate on behalf of Israel.
Restrict your arguments for Israel, to those which demonstrate support for Israel as flowing from broad principles that your interlocutors claim to uphold. Do not present any arguments suggesting that an exception to those principles should be made for Israel.
First is the category of argument claiming that Israel deserves support because an exception should be made to broader principles. The most significant argument in this category is the covenant between God and Abraham. Consider what it would mean to make a general principle for this argument. It would mean that any people who claims that their deity made a promise to their ancestor(s) would have carte blanche to do as they please to its neighbors. Is this a principle you would support? I didn't think so. Therefore, the only way this argument could have any effect is if it convinces the listener that whatever his principles, the Jewish God's promise thousands of years ago should take precedence.
Now for a few arguments that marshal broader principles into support for Israel.
Indigenity. One of the principles often cited against Israel is "indigenous rights" with the claim that the Palestinians while the Jews are not and thus Palestinian rights must be respected. The counterargument would be that indigenous rights are meaningless without a definition of indigenity such as the Martinez-Cobo criteria. People are free to have their own definition of indigenity that applies to all claims of indigenity, however, anyone insisting on an alternative to Martinez-Cobo can be challenged on the grounds of where else that alternative is accepted. From this argument, unless one believes that conquerors can become indigenous, one would have to accept the Jews of Israel as indigenous and that indigenous rights apply to the Jews.
Legality of the "settlements." There are two issues involved in this one. One is how far does Israel's right to possess land beyond the 1949 Armistice Line extend, the other is what right Israel has to settle land that is not recognized as permanently Israel. As to what rights to the land go to whom, the notion that Israel's land rights should be limited stems from the principle stated in UNSC 242 about the inadmissibility of acquiring land through war. The problem with that notion is that the application of it to say that the full plot of land past the Armistice Line thus "belongs" to the Palestinians effectively confers its blessing on Jordan's acquisition of territory through war back in 1949. This does not mean that there are no grounds for the Palestinians to achieve autonomy or even sovereignty on some part of that land, however, if you believe that acquiring territory through war is inadmissible, you have to admit that a foreign army's conquest of the land 66 years ago does not confer an automatic right. Regarding settling the land before it is internationally recognized as part of Israel, the principle should be that civilian settlements are either legal for all occupying powers or illegal for all occupying powers. There has not been a single ruling from any international entity that civilian settlements occupied territories are illegal when done by any power other than Israel.
Civilian casualties and terror. The principle of just war is that there are certain provocations that constitute a legitimate casus belli. Without getting into what cases belli are legitimate in the conflict, when there is a legitimate casus belli, action is permitted to impede the ability of the offender to commit the provocation. Any action taken solely to impose a human cost for the provocation, such as one directed at individuals who are innocent of the provocation or so untargeted as to have a greater likelihood of hitting an innocent target than on responsible for the offense, is an act of terror. However, action directed at those perpetrating the provocation is not an act of terror. When such an action ensnares innocent victims, it is possible for that action to be lawful or unlawful depending on the circumstances, but in either case it is not terror. You can summarise this as, it doesn't matter whether the innocents killed are Muslim, Christian or Jewish and it doesn't matter whether those killing them are Muslim, Christian or Jewish, if the innocents are the ones targeted or there is no targeting, it is terror, if they are not targeted, it is not terror.
There are a slew of other issues where such reasons could be applied. The important thing is whatever reason is invoked to defend Israel must be one you would allow to be used for any other group in relevant circumstances and preferably one which would demonstrate that whatever reason is invoked on behalf of the Palestinians would not be invoked on behalf of anyone else.