It's easier than you think!
No one should be intimidated about flavoring alcohol. It is a simple process that gives great results and allows one to put an individual mark on what you drink.
The possibilities are endless and can be as simple or complex as you like.
I offer up a few basics to lead you down the path and from there you can take off.
Please note that while the term infused is used quite commonly, but it really refers to the process of imparting flavor WITH heat, while macerating is generally what is being done these days.
You begin with the base spirit you will flavor. The choice is yours. Vodka offers a neutral base but do not rule out rums, bourbons, vermouth. They all can be enhanced with a variety of fruits, herbs, and botanicals. Now while I do not like to advocate for using bottom shelf liquor, there is no need to break the bank either. For instance Svedka or Smirnoff are perfectly appropriate vodkas to use for this.
I like to to use a vodka when I am simply experimenting or want to limit the flavor profile to the additive. If I am creating a specific drink and know that bourbon will be the high note, I will use the specific spirit.
Herbs such as lavender, rosemary, basil are common additions. Fruits from citrus of all kinds, to berries, to pineapple , to lychee are all plausible. Choose your desired fruit. Organic is always better in doing this. Don't forget peppers, especially hot ones, too. Fresh botanicals and spices are of all kinds open up the palette to zillions of variations, peppercorns, anise, coriander, bay leaf, lemongrass, ginger to name some.
The storage jars should be washed clean and dried, with air tight lids.
Place the desired flavorings into the jar, cover with the spirit, and give it a shake. The time for macerating varies with the produce used. From several days to several weeks depending. Shake on a daily basis, don't be afraid to give a taste either. Once at the desired strength, strain and transfer to a clean bottle or jar. Throw out the fruits, herbs, etc. The fruits, once macerated, have been zapped of their sweet delicious flavor, as you may discover when you try to bite into that pineapple chunk that has been sitting in Cachaca for two weeks. It has a very strong and bitter alcohol taste.
Below I have given a few tips on the prep of various items and a genera rule of timing.
Prepping the ingredients
Strawberries should be washed, stems & leaves removed and sliced
With citrus use the peel/skin with as much of the pith removed as possible
Pineapple, mango, cut into chunks with skin removed
Herbs can be used in their entirety
Vanilla beans sliced lengthwise
A general rule for timing
3-4 days for strong, intense flavors (vanilla, citrus, basil, thyme)
1 week berries, mangoes
2 weeks mild flavors such as pineapple , ginger, lemongrass
Remember this is experimenting and supposed to be fun. Don't be afraid to try different combinations, and do not be afraid to have a few failures as well.