If you want to bet each way you do it with a bookie in fields of eight horses on short priced favourites that you think are value.
The longer the odds of the horse, the poorer value an each way bet is.
Similarly the bigger the field the worse value an each way bet is getting one quarter odds for the place.

With trifectas you must beat the market. There are no hard and fast rules but if there are short priced horses in the race I'm only interested if I think the short priced horse has a good chance of missing the place.
I don't have hard and fast rules - but I like to avoid favourites. If you base your trifectas around favourites you must lose on the tote.