I always used to struggle with mayonnaise, but now I have a stick blender and life is gooood!
In a tall thin jug (ie the one that probably came with your stick blender), whizz together half of the salt and everything else but the oil. Add the oil in a very thin trickle to begin with. Once the mixture begins to thicken, you can add more oil in a faster stream until it is all mixed together and blended into something that looks like mayonnaise. Have a little taste, and if you think it needs more salt, add some.
That's it. Told you it was easy! It should last a few weeks in the fridge, but in my house it always gets used up before that happens!