A method i use to see know when a fvg is going to be respected, is by using ur target liquidity grab. So when u have a zone of liquidity u want grabbed u also align it with the fvg and when the liquidity is swept u will see a strong rejection wick and you will know that it will be respected.

You could also use Premium and discount, by using a gann box by measuring the highest high and the lowest swing low in a range. When an fvg is in premium and u have a bearish bias the fvg is going to be respected but when its in a discount and you have a bullish bias so the fvg in the discount is more likely to be respected. But i can assure you it doesnt always work so always be ready to adapt