Well, the basic and older one is to hunt. Find a hunt suitable for your level and skills where you can get a lot of rares and/or creature products. Some creature products are a lot more valuable nowadays that they can be used in weapons and armors inbuiments.
imbuements.
Also, you can try something like "stock trade" on Tibia. You can buy Tibia Coins, usefull useful creature products or items for x, then sell it for x+y. Some friends made tons of gold doing this.