The first step is generally to replace the porch light switch with a UPB switch, unless you're trying to do something tricky like split out the switch... If it's wired into a different circuit but you want it controlled by that switch, that's entirely possible too using Links.
With Landscape lights, often times there's a place inside where you can mount a timer - well it turns out a UPB Appliance module fits in there too, so you can get your landscape lights on UPB control pretty easily - even if you don't have that, you can usually use one outside the transformer to power the transformer as a whole.
Once everything is on UPB control, it doesn't matter much how it's wired - you have a lot of flexibility in how the switch works - you can use a single rocker that controls the local load and sends links, or an example of my back yard - single rocker is wired to my porch light, but if I double-tap that switch off/on it also controls my landscape lights. An alternative could've (and will someday) be to put a US240 in there so I can have a half-rocker for the main lights, then separate rockers or buttons for the side yard lights and the landscape lights all separate. UPB is very flexible.