I haven't had as much experience with liqueurs as I would like, but if you're looking to get something that's around 20-23% ABV, you'll probably want to make/get some fruit purée/juice, then up the gravity using sugar. There are a few great distillers' yeasts out there, so if you want to get it to 20% or so without distillation, you can use a distillers' yeast like Wyeast 4347 Eau de Vie
and it'll get your mixture up there. And seeing as the yeast won't survive past 21% ABV or so, once fermentation is complete, you could definitely backsweeten it to your taste.
Another good option is to basically make a fruit wine (using pretty much the same techniques described above) but to ferment with wine yeast (like montrachet champagne or something) and then do a little freeze distillation. That way you can just freeze it for a little while (not until the whole thing is frozen), decant off the ice, and keep the remaining liquid.
Of course the easiest way to get around this is just to make infused vodkas. They are amazing and wonderful and all you really need is some vodka, fruit/spices/flavorings, some containers (mason jars are good for experimenting) and a really small amount of time (usually only around 2-4 weeks). Easy peasy lemon squeezy...but those will be the strength of vodka (but they won't taste like it).
Read my homebrew blog!
Sea Symphony American Barleywine, Smokey the Amber
Figgy Pudding Ale
Scarlet the Galway Girl Irish Red, Limerick Session Stout, Junior/Senior Amarillo RyePA, Ralph the Partigyle Bitter
1839 Westminster Porter, Golden Gate CaliCommon, Autumnal Saison
Relax, don't worry, have a homebrew.