1948 War - Israel had a very organized and well-trained military, with experience during World War II on top of fighting the British and the Arabs, and as others have said they had acquired Western weapons. The Arabs didn't have much in the way of numerical superiority. All the Arab nations, except Jordan, had weak militaries and in case of Syria and Lebanon had just came into existance. Iraq and Saudi Arabia were too far away to offer any serious help (and they didn't had much interest in doing so, in any case). The Arabs were disorganized and divided amongs themselves, with Jordan actually secretly approaching the Israelis for a settlement.
1967 War - Began with an Israeli offensive, which destroyed the bulk of the Arabs' air force on the ground even before they can fight. The Israelis had a clear plan of what they were doing as opposed to the Arabs who were generally disorganized and failed to coordinate their attacks.
1973 War - As others have said, the Arabs (Egypt and Syria only, not Jordan) failed to capitalize on their initial surprise. The Israeli had been prepared for this and had an ability to quickly mobilize its forces and did so. Israeli forces were much better trained, led and motivated than the Arab forces, and the Arabs soon loose the benefits of numerical superiority once Israel fully mobilizes.