Rain = Good
I love Ludicolo. But that doesn't mean that everybody does. I can accept that. I think that one of the reasons he is not well played is because people don't understand his strengths.
Both of his abilities only work in rain.
If you are serious about playing the character you will need to keep this in mind.
Swift Swim allows him to be a Rain sweeper while Rain Dish gives him a a free second Leftovers.
But he can work without it.
Albeit not as well.
I find it hard to really give a comprehensive example of this, in so far as far as strategies for winning go, but I will say that it is possible. You can win, I mean, not amazingly well, but he can do it.
Probably the best bet would be a special wall, as Grass / Water is a pretty interesting typing. Unfortunately not very many resists, but his weaknesses (except for Flying) aren't exactly super common.
You can use either Synthesis or Giga Drain as the Insta-heal. Synthesis is good because it's a set amount, but Giga Drain is also good because it deals damage.
It's up to personal preference.
Surf is there because dealing damage is good, and Water is a pretty good attacking type.
Also to make sure Ludicolo doesn't just get Taunted and be unable to do anything, especially if you choose Synthesis.
If you run Giga Drain, though, it might be useful to use Rain Dance to guarantee the Rain Dish extra HP.
Just don't use Rain Dance and Synthesis, because rain makes Synthesis preform worse.
Maybe you won't use him in you main group. But he is worth playing. And if you are like me, and don't mind making a fun group, you may make one focused around him.