How to tell if your plant is ready to be watered:
Check the soil. Absolutely most important! If the top of the soil is dry, stick your finger in as much as you can, being careful not to disrupt the plant too much. If it still feels dry, then your plant is probably ready! Do not water if the top of the soil feels wet/moist.
Monitor the weight of the pot. This takes practice to get a feel for, but over time as you care for your plants, notice how heavy the pot feels. You'll get used to how light the pot will feel when the plant has used up its water and is ready for more.
Look at the leaves! Touch the leaves often. Especially if they are more succulent plants, those leaves will tell you a lot. Notice the color and shape. Many foliage plants will droop or get paler when ready for water.
Water should be warm and run it on slow!
Slowly soak the plant, being careful not to spill too much soil (more for your sink's sake!)
When water starts to drip out the bottom of the pot, keep running the water in the plant for another ~30 seconds or so.
Set aside. Do something else (like water another plant).
Go back to your plant and run the water through it again, same process as before. The first soak was to moisten the soil and ready it for watering. The second soak was to actually saturate the soil.
Remove from watering area and put back where it goes!
Get an individual dish that's bigger than the pot you're watering.
This is like cereal. You can put the pot in first then add water or add water then place the pot in. Play around with what feels good to you!
Let the plant soak up the water from the dish.
It is done when the top of the soil is wet. If this doesn't happen after awhile, you might have to top water a little to finish it off.
Don't leave the plant sitting in water for too long. I'd do an hour tops.
Bottom watering can help if the soil has dried out so much it's too compact and top watering isn't working.