This is more complex than you might think
And this is a bit of a frame challenge. Collecting rainwater off an ocean would be no small thing. You can't just suck up the top tenth of an inch (even if you knew where the rain would fall). So this presents a more practical solution.
Also, the question changed after this answer was posted....
Climate is complex. When Douglas Adams said (tongue-in-cheek) that space is really, really big... that's how you should think about climate's complexity. It's really, really, complex.
So, let's throw technological limitations out the window and think about this problem.
Your target location is important. Watering a sea-level desert is different than watering a high altitude desert. But I believe your options are similarly limited.
Volume is your biggest problem
For example, Kansas City, Kansas in the U.S. gets an average of 39 inches (992 mm) a year. Kansas City (if we only consider the boundaries of the city and not any of the surrounding region) is 319 miles2 (826 km2). So, in one year we're talking about 0.2 cubic miles (0.82 km3) of water or 2.2e11 gallons.
That's a lot of water.
But that's what you'd need to move to duplicate the rain in Kansas City. You're not going to do that with boats.
Which means transportation is your next problem
If we want to toss realism to the wind, you could move all that water through an 8" (25mm) pipe with enough pressure. The pressure would be so high that it would probably initiate fusion or change the orbit of the earth or some other reasonably apocalyptic consequence.
Using this handy dandy pipe volume calculator and ignoring things like pressure, a 24-foot pipe will move 9 billion gallons 500 miles.
We would need 24 such pipes to move all the water we need, or we need a lot of pressure.
Next is desalination
The wonderful thing about the natural rain cycle is that it leaves the salt where it belongs, in the ocean. As it turns out, manually removing salt from saltwater is a glorious pain in the caboose. But we're ignoring tech limitations, right? Each of those 24 pipes would need a substantial (really, really, really big) desalination plant and you'd need a way of getting rid of the salt.
That last part is really important. You see, Mother Nature is leaving the salt behind over the entire surface of the ocean. In other words, the overall salt density doesn't meaningfully shift thanks to evaporation because She's drawing from so much water in the first place.
The effort of filling plane-after-plane with salt to gently spread it like your grandmother's ashes over the ocean would be... economically challenging. How to get rid of this much salt without bringing to pass a zombie apocalypse would make for a great second question!
Next is distribution
The easiest solution would be to let the water fill natural lake areas. This could be problematic as the initial erosion would be magnificent. However, it would basically work — but it's leaving the pooling of water in great enough quantities to create a local rain cycle up to the vagaries of natural geography. You'll probably need to help it along by creating a lot of dams.
Which don't always work. Remember how much water we're talking about! And remember that large man-made lakes like Lake Mead have had very little overall impact on the creation of new farmland — through rainwater. They've had a huge impact through the availability of irrigation.
Therefore, I recommend this route.
But if you want to be a bit more... fantastic...
I personally like the idea of pumping the water to the top of a mountain and pushing it through a honking bit sprinkler head. Twenty-four heads surrounding an area the size of Kansas City spraying out water 91 days of the year (which is the average number of rain days for Kansas City). It would look cool! It would create rain!
And it's about as technically feasible as building a stairway to heaven.
But I'm not a fan of technologically-feasible answers unless you've used the hard-science tag. Don't use that tag.