Ways you can encourage this when your children are young are:
*Encourage them to speak to their teacher about questions concerning their homework or test results, and how they can do better.
*Encourage them to speak to their principal regarding opportunities to help out at the school.
*Encourage them to speak to their coaches as to why they aren't playing or strategies, asking how they can improve their game.
*Give them advice as to how to "tweak their style" as I call it. Sometimes it IS just a "tweak," a little change.
It is important to teach your children to speak to others they don't know when you are around, so they are comfortable with speaking to new people.
Now that my children are older, it is a delight to see them seeking advice from people they know are knowledgeable in certain fields before they make big decisions. It is great to see them get wisdom from a variety of (very wise) sources before just using their own judgment period.
Proverbs 12:15 The way of a fool is right in his own eyes: but he that hearkeneth unto counsel is wise.
Challenge: Teach your children to seek our advice. Teach them to value the input of others. Far too many young people learn to scorn others' input into their lives. I have seen many parents undermine the advice from others and belittle others for some reason. It is a wiser parent that teachers their children to take advice from wise people.