Being able to learn the time successfully relies on a child being able to count to 60 and at the same time, learning the five times tables. Start by making children aware of time. If it's at home, tell them the time when they get up in the morning. Tell them what time it is when you eat supper, when you send them to bed, and so on. If it's at school, tell them the time when the school bell rings, etc. Teach in incremental steps:

1. Teach the "o'clock" concept first, whilst ensuring that the counting to 60 and the five times tables are being learnt.
2. Use visual aids such as an analogue clock that you can manipulate which will also teach the concept of the "big" hand and the "little" hand.
3. Use a paper plate to teach the half and quarter times. Fold the plate into four and let them write the relevant numbers. If they are small children, let them trace the numbers from cut-outs - as long as they know which numbers are which.
4. Teach one concept at a time. After mastering the "o'clock," do the half past before attempting the quarters.
5. When ready for 5 minute increments, let them color the twelfths and use a pencil or crayon as the hands.  
6. Talk about time at every opportunity.
7. For digital, explain am and pm. Use associations to ensure they understand. Many children have digital watches but fail to understand the actual meaning of the numbers, except that they are numbers.
8. Explain that the hour comes first - the opposite of analogue where we always identify the minutes first. 
9. Again, go in incremental steps. 7:00, 8:00, etc before adding minutes. The cross over between analogue and digital is the most difficult and children confuse the hours and minutes so make sure that the hours and their position on the digital clock are recognized before adding the minutes.

Practice is the key element and regular discussions about time will ensure their relevance.