What is the best way to increase yields per hectare?

There are many yield-affecting factors when it comes to farm management including irrigation, nutrients, weeds, insects, diseases, etc. So, optimizing each of those factors can help increase your yields per acre.

But, it’s important to remember what your real objective is. For example, some management decisions may lead to a higher yield-to-acre ratio, but the required inputs/costs to achieve those higher numbers may result in a less profitable outcome overall for your operation. So, understanding the costs versus benefits can help farmers achieve a yield-to-acre ratio that’s optimal for their particular fields and circumstances.

Since you categorized your question as being related to corn, you may be interested in checking out some of these resources I found here on AgFuse: how yield champions use cover crops to increase their bushels, what steps you can take to protect corn yields after having planted cereal rye, and how crop scouting apps can actually help you increase yields. 

Start by taking a good long look at your soil fertility. Get a reputable soil test done and determine what nutrients you need more of. After that, try to provide those nutrients in a good form for the plant. Liebig's Law of Minimum is a great way to visualize a plant's nutrient needs. The plant will only produce up the level of it's most limiting factor, whether that's nutrients, water or something else. So make sure you provide the plant with everything it needs to be successful.