This Tin Ore farming guide will show you the routes that I use for farming Tin Ore in Classic WoW.
If you want to farm different ores, please see my other guides:
Copper Ore Iron Ore Mithril Ore Thorium Ore
Low-level characters should skip the two caves marked with red circles.
Low-level characters should skip both caves and stick to the east side of Redridge.
There is more Tin at the southern route, so you should start there. But, you can use the northern route as an alternative if there are too many people farming in the zone.
The respawn rate should be fast enough that you don't have to enter the cave marked on the map, but there is always two Tin Veins inside, so I think it's worth to go inside with high level characters.