Different plants, different root depths
Some plants have roots quite close to the surface whereas others are deeper into the soil. Those deeper ones will require more water in order to reach the roots. A little research into your plants will help you get the information you need to judge this for yourself.
Adapt to the weather
If there's been a good amount of rainfall reaching your containers, you may not need to water them. On the flip side, if it's very warm and sunny, your plants may require more water than usual.
Be consistent
It's good to give your plants a steady amount of water, creating a routine so that you're giving your plants a similar amount of water at a similar time of day. Early in the morning or late at night are both good times as plants are likely to absorb more water, whereas during the middle of a hot day, water will evaporate more and therefore the soil will absorb less.
It's all about that base
Water around the base of the plant, rather than directly onto it as it is the roots that require the water rather than the leaves. In fact, wet leaves can encourage fungal problems.
Be gentle
Watering your plants too quickly or roughly could cause the water to splash soil onto your plants.
Mulch your containers
You can spread mulch around your plants to enrich and/or insulate the soil. This will also prevent your top layer of soil from drying out as quickly.
What pot have you got?
Some materials retain water better than others. For example, plastic pots retain water much better than terracotta pots.
Do the knuckle test
Soil may appear dry but if you put one of your knuckles into the soil, you may feel a good amount of moisture just under the surface. This will help to prevent you from overwatering your plants.