You can use eye drops as often as necessary through the days, for example every hour, although every few hours is usually sufficient with newer products. If you need to apply them more frequently than four times a day and over the long term, choose a preservative free version. This is because our eyes can react to preservatives and aggravate dry eye symptoms.
As a general rule, if eyes are dry in the morning after the eyes have been closed overnight, blepharitis is the problem. If eyes become dry throughout the day, then evaporation of tears from the eye's surface is the cause.
Finally, if an eye drop doesn't seem to be helping, choose another with a different lubricant. It can take trial and error to find the drop that is right for you.
To insert eye drops, gently pull down the lower eyelid and squeeze the drop into the pocket formed. To stop the drop flowing away, close the lid for ten seconds and gently apply pressure to the inner corner of the eye for at least a minute. This stops it draining into the nose. You only need to insert one drop, any more than this and it will be diluted or overflow. Wait about thirty minutes before inserting another type of drop.
Eye ointments are applied in the same way, by squeezing a small amount into the pocket formed when the eyelid is gently lowered. It should melt rapidly and blinking helps to spread it.