“But continue thou in the things which thou hast learned and hast been assured of, knowing of whom thou hast learned them;”  
2 Timothy 3:14

Be assured of the realities in God’s word, be fully persuaded that they are true and walk in their realities. It’s not enough to hear God’s word and like what you hear or like the preacher who’s preaching it, you have to be persuaded by the word of God unto action and insistence as you walk in that reality. He tells us:
“He staggered not at the promise of God through unbelief; but was strong in faith, giving glory to God; And being fully persuaded that, what he had promised, he was able also to perform.” Romans 4:21
Abraham was strong in faith, refused to stagger through unbelief, instead he gave glory to God because he was fully persuaded. That was not the case with the children of Israel that left Egypt with Moses:
“So we see that they could not enter in because of unbelief(‘unpersuadable-ness’).”  Hebrews 3:19
In your persuasion, be fully aware of who you are learning from, here he isn’t talking primarily about the person who’s bringing the word of God to you, but the word of God himself, that’s why he says in the next verse:
“And that from a child thou hast known the holy scriptures, which are able to make thee wise unto salvation through faith which is in Christ Jesus.”  2 Timothy 3:15
It is the holy Scriptures, the word of God that is his primary reference, he says continue in the word, being fully aware of (what) the word (of God has done, is doing and can do).
The word of God is able to make you wise unto salvation, this means as you continue in what you have learnt, the word can give you the wisdom you require in whatever situation you’re in so you can save yourself from the bad into the good or be promoted from the good into the better.