The red berries is scattered around the bushes that are scattered throughout the Runescape. These red berries are a good source for RS gold sell.
Source: wikia
Pick red berries and get more RS gold
The red berries can be used to make dyes a red berry pie. Although these berries are used in Cooking, they are not edible unless you turn them into pie. These can also use to make Ranging potions. These berries are pretty much valuable and can give you more Rs gold be selling them at the Grand Exchange.
This method of picking red berries is simply and easy enough. To get started, you will need at least 50 to 100 law runes, 150 to 300 air runes, a fire staff and an explorer’s ring (get some enough RS gold in order to buy the necessary items). You also need at least level 25 Magic Skill to use the teleport to Varrock. Equip both the fire staff and the explorer’s ring.
To start picking the red berries, you can find them at the south of Varrock. Pick all the red berries on the area. Use the explorer ring to teleport back to the cabbage patch near Draynor. There should be another red berries at the Draynor Pig pen. Wait for 100 seconds in order the red berries to be respawn. Repeat the process once they respawn. Once you have a lot of red berries, you can now sell them at the Grand Exchange to gain more RS gold.