Are you asking for good sets of 10 to play with, or strategies (combos using cards from just these two expansions)?
Most people on here prefer playing with random sets of 10. If you've already played with base a decent amount (say 10+ games), maybe try playing a few random Seaside only games first (using the 7 basic cards from the base set, of course), to get a hang of the new Seaside cards. One thing you can do is play with 10 random Seaside cards, then play with 10 random new ones that you didn't play with in game 1, then play with the remaining 6 cards and with 4 cards that were not bought or didn't figure in prominently in the first and second games (or just use 4 base set cards).
Moreover, the Seaside rulebook has a few recommended games, including some that are matched with the base set, so you could try playing those, though I generally never bother (I think the only recommended game I've played is "First Game" from the base set).
The fun in Dominion though, is the huge variety you can have, and a good way to see a lot of these is random set ups (and you and your fellow players can choose to reject any setups that you think are too similar to something you've already seen, but my friends and I never really do that unless there's a specific card we're not in the mood to play with or something).
Now, if you want to know about strategies (combos), I recommend trying to discover some of these on your own, at least initially. But one powerful combo that can be found in Seaside only is Fishing Village/Wharf. A combo making use of both expansions is Haven/Library. Haven is effectively reducing your hand size (you can save up useful cards like terminal actions you can't play yet, such as extra libraries, or small money like copper), so if you play Library after it you can draw more cards. This just gives you an okay hand this turn, but if you saved up even some minor cards, your setting up a stronger hand next turn. Combined with a source of +2 actions (Festival and Native village are probably best for this), you can get some real power out of this combo, as Festival's especially will help you pick up Havens with their +buys; I haven't really tried this much though so it may not be all that great. Another cool combo is in a game with Ambassador, where you're frequently drawing your whole deck, you can purchase a single curse and then use Ambassador to give out curses. However, don't return your curse to the supply unless the game is ending soon or there are no more curses left; of course in other situations where you're naturally gaining curses, you'll usually want to return them to the supply.
As far as counters, Militia and Ghost Ship are effective against Warehouses. Speaking of Ghost Ship, if you have a Tactician and you get hit by a Ghost Ship place two good cards (other than the Tactician) on top of your deck, then use the Tactician. So Tactician is an effective counter to Ghost Ship; in fact the Ghost Ship can end up helping you! Another counter is Lookout, which can help neutralize Sea Hag a bit.
Most of these strategies are discussed on the Dominion strategy blog, but I just thought I'd mention them again here. I hope that helps, and have fun playing with Seaside.