To earn easy weapon skill, go and get any two cars and place them in your Grove St home garage. Then with the weapon of your choice shoot the cars until they are nearly on fire. Then walk away from the garage so it can close. Walk up to the garage again and you will notice that the cars are repaired. Repeat this process as it is one of the fastest ways to earn weapon skill in the game. To check your progress with weapon skill, switch to the weapon that you want to check and then go to STATS in the menu and then go down to WEAPONS. The number there is how many skill points you have. You need 1000 skill points to reach hitman level.