Avoid Random Battles
Once you learn the cut ability, you can teach it to some of your Pokemon. This ability will allow your Pokemon to cut down some trees and also eliminate high grass in grassy areas. This will prevent any sneak attacks from enemies to help you avoid random encounters. The grass will return whenever you leave an area and return to it or save a game and load it again later.
Freeze the Game Clock
You can freeze the game's clock to keep it set on a certain day and time. Head to Vermillion City and find the Machop stomping the ground. Talk to him and then view the coin case in your pack. This will cause the game to either reset or freeze. You will have to reset them game if it freezes. When you return to the game the clock will be frozen at the time at which you looked in your coin case.
Find Items Easily
Go to Ecruteak City and speak to the man in the house directly east of the gym. He will give you the Itemfinder, which you can use to find potions for health boosts, genes for your Pokemon and more useful collectibles. The Itemfinder will uncover items only on the screen you are viewing. Check an area fully by moving around while using the Itemfinder.