How can I make mocktails that actually taste like non-fruity cocktails?
You're going to want to look for classic cocktail recipes and mixers. Get a base of cocktail knowledge, then fill in the alcohol with a nuetral filler. Teas and smokey coffees can replace the flavor profile of some bourbon or scotches. Club sodas or flat tonics can replace some grain spirits. Angostura, orange bitters, vermouth, tinctures, demerara syrups are all classic mixers you'll want to use... usually Imbibe Magazine has some pretty good resources and make-your-own bitters and mixers. Sometimes Bon Appetit has a good classic drink. I know a couple months ago they explained how to make your own vermouth. 

Another good resource is to find a local cocktail bar that simple specializes in high end cocktails and just talk to a bartender. They'll have lots of knowledge and resources to share! 

A website I like to use sometimes is Cocktail Codex.