The best thing for you is to be able to play humans who are better than you. Unlucky for me, Im stuck playing my brother and friends who well...stink. One of my friends beats me sometimes but its only cause hes Marth and I still stick with Ness vs his Marth xD.
Anyway its actually smart to do what you did with Ice Climbers, split them up then go for Nana xD thats what I do. PK Fire is really good against them, and they really arnt that hard to beat (unless they chain grab you) Plus Blizzard gives you lots of health, especially if they double it up on you.
Finally to help be unpredictible be a little sparing with you pk fires and thunders. I used to just throw them out at random times hoping they would hit sometimes, and it was actually kinda hard to stop that. Pk thunder mindgames work good, and flooorblasting is helpful too to switch things up.If you having trouble with mind games, try tailing them a bit more. also be sure to always move the PK thunder like a snake, and not just aim straight at them (unless you expect them to dodge and want to punish their dodge with a PKT2, or something like that.Sorry if you know this stuff already.) Finally (unless your playing a Ness, Lucas, or G&W) throw out a PK Flash sometimes. Not too often, maybe just once or twice. It actually works sometimes xD
of course, im not the best ness player or anything, these are just some tips. Develop your own PK Style!
By the way, this is a really weird coincidence but I played Ike and now play Ness as well! Thats really weird cause its similar with a lot of ness mainers xD