Farming gold is one of the basic skills that one needs to learn to excel in DotA. Farming simply means killing monsters, creeps and neutrals to get and accumulate gold.
Farming Techniques
The most important skill in farming for gold is the ability to Last Hit. Players only receive gold if they deal the killing blow to a creep (or hero). That's why it's crucial to wait until the enemy unit's HP is low before attacking or using a spell.
This strategy is most frequently utilized early in the game, during which last hitting competes directly with denying creeps, although it should be practiced throughout the entire game to maximize farming efficiency.
Some heroes are better at farming for gold than others, particularly those with an AoE or Area of Effect spell. Examples are Pugna's Netherblas and Leshrac's Lightning Storm.
For such spells, one needs only to wait until many enemy creeps have low HP before casting the spell. This is done by attacking enemy creeps that allied creeps are not currently engaged in battle.
Aside from skills and items that give extra AoE are commonly used for framing. Examples are Cleave from Battle Fury and Radiance, which is undoubtedly the best farming item in the game. Shiva's Guard deals damage to every unit in a large area; when coupled with another AoE spell, entire creep waves can be quickly destroyed.
Farming creeps is pushes a lane faster than desired. That's why the best position to farm is next to an allied tower so you can be close enough to retreat safely but far away enough so the tower will not steal the Last Hit.
Maintaining the position of the creep line and not pushing is therefore crucial to safe and efficient farming. When farming for gold, always remember to avoid using damaging spells and focus on getting the Last Hit. Furthermore, friendly creeps must be denied whenever possible to prevent the allied creeps from pushing towards the enemy's side.
Although farming for gold tends to be boring, it's important that you practice patience and frugality to ensure that you'll have enough to buy the high priced items you will need to become powerful.