Andrew Schloss has published a great guide to this hobby in his book Homemade Liqueurs and Infused Spirits. I've had plenty of versions of homemade limoncello made by friends, and while most of them were perfectly palatable, they all suffered from a lack of lemons actually grown in the Amalfi coast, or maybe I'm sorta nostalgic and provincial that way. Once you've sipped limoncello in Positano, pretty much everything else is just a poseur.
Schloss doesn't even bother with a simple limoncello recipe, since most versions are just pure grain alcohol or vodka with lemon juice and zest in them aged for an indeterminate time. In fact, his recipes aren't necessarily for liqueurs, but rather tinctures, since liqueurs are technically distilled directly from the sugars of the fruit. And that, as we know, is illegal at home. Instead, his tincture procedures involve mixing chopped fruit and sugars with various liquors as a base spirit. It's unusual that Schloss employs bases other than the easy neutral grain spirits, and his use of rums, bourbons, vermouth, wine, etc., makes the resulting products a lot more interesting.
Since sugar is an important part of making fruit liqueurs (the term which we'll use for simplicity's sake), Schloss also includes a section of recipes and procedures for making some interesting simple syrups like Brown Cow Simple Syrup and Coconut Cream Simple Syrup that are useful in liqueurs as well as in cocktails or teas.
Not limited to just fruit, chapters focus on vegetables, nuts, herbs and spices, coffee, tea, chocolate, creams and caramel liqueurs, so odds are you'll find a few flavor combinations which will encourage you to get out a few mason jars and start steeping. Schloss also includes copycat recipes for famous liqueurs like Chambord, St. Germain and Bailey's, in case you want to try to make your own versions at home.
Since liqueurs traditionally contain a bit of sugar, they are generally best served as an apertif or digestif since they can be overpowering ingredients in most cocktails. Schloss does have a section on infused liquors which are more appropriate and versatile as cocktail mixers. You can take a relatively inexpensive bottle of hooch and convert it into much more interesting infused liquors like Black Pepper Vodka, Cucumber Gin, Horseradish Schnapps, Minted Bourbon or Orange Rye. I've already started making up my shopping list.
Finally, Schloss includes 80 recipes for torqued-up versions of traditional cocktails that employ the other liqueurs, brandies, infused liquors and simple syrups in the book. I look forward to dressing up some Bloody Marys, Manhattans, martinis, old-fashioneds, screwdrivers and sidecars in the future.
Most of the recipes take only about a week of steeping before you're ready to strain and bottle them, so there's not a huge investment of time or money. Homemade liqueurs would make excellent hostess gifts or your contribution to a pool party, so there's still plenty of time to pick up the book and start crafting your own signature drinks. Save me a dram or two.