What is the best time to enter and exit a trend?

Check main trend in H1/H4 interval, identify swings, find biggest retracement in last swing, then try to join trend on next retracement of the same size. This would work for swing trading.

Maybe it will be easier to understand from picture, check fresh example from eur/aud

The best time to enter and exit a trend is when the trend change occurs. Traders identify the trend change with the help of moving averages.

This is a clear example

Apparantly, the theoretical answer to the question of when to enter the trend goes like this: the best time to enter the trend is in its very beginning. However, as ussssual, theory doesn't coincide with the practice. It is really hard to determine when the trend is going to change in order to have enough time to enter it. That is why the most experienced traders trade against the trend in hope that it will soon change. Such a trading style requires lots of knowledge and experience from the traders. That is why newbies are recommended to trade according to the trend. Surely, you'll not get as high profits as successful trading against the trend, but you'll not lose all of your budget.