Well I can't make a team for my life and i get surprised by pokemon that i never encountered for example Stallrien .....
Hmmm... nothing can be done about the second part. You learn through practice. The more you battle, the more you can predict move-sets and how exactly some Pokemon are used (barring noobs who use totally off-beat movesets, in which case even I can be surprised).
But the first part is relatively easy to fix. I've often used a basic framework for any team, as in, there are certain elements you really MUST have, and I'll see if I can remember them. It also depends what kind of team you want to run, as in 1.) a sweeper team 2.) a stall team (like what I use), or 3.) a mixed team.
A pure sweeper team is a team comprised of all sweepers; an example of this would be a team composed of Garchomp, Alakazam, Metagross, Heracross, Charizard and Weavile. A team like this relies on simply massacring the enemy and trying to do it as fast as possible. These teams tend to be extremely hard to pull off with the existence of Blissey, Skarmory, Bronzong, and the likes.
A pure stall team is my personal favourite, and an example would be something like: Blissey, Skarmory, Dusknoir, Claydol, Miltank, and Milotic. Some would argue Milotic and Miltank, since they can dish out some decent attacking power, but for the most part, a pure stall team is a team that relies on prediction skill and annoyance, and for the most part picks away at the enemy until they're down.
And a mixed team is more common, composed of both walls and sweepers. This is the type to shoot for if you're more of a beginner. And in this case, you need a few basic things:
1.) A special sweeper
2.) A physical sweeper
3.) A special wall
4.) A physical wall
These four can sometimes be combined, like with Milotic being a dual special wall/special sweeper. Metagross can sometimes make a dual physical sweeper/physical wall. Miltank can make a good dual special/physical wall AND can dish out some good physical power. So play around with these combos all you want.
Now, this is slightly basic. But there are a few more elements you absolutely NEED for a successful team (and by successful, I mean a team you can use consistently and win with).
5.) A Flyer/Levitator - the single most common and predictable physical move out there is Earthquake. Great power, and great type coverage... except against Flying types and Pokemon with the Levitate ability. So, to prevent some douche like Garchomp from ruining your day, make sure you carry something that is immune to it's most powerful STAB move.
6.) A Spiker/Stealth Rocker - Spikes and Stealth Rock can get annoying; make use of it.
7.) A Rapid Spinner - Spikes and Stealth Rock CAN get annoying; make sure you carry something to get rid of them.
8.) A Ghost - This is more optional, but a Ghost can be extremely helpful for completely blocking Fighting moves and Normal moves. Not to mention Explosions; nothing, and I mean NOTHING is scarier than going up against a dying Metagross that's looking to Explode, and viably massacre one of your Pokemon. A Ghost Pokemon can completely screw over your opponent in this case.
That's about it, and I've got to go, but if I think of anything else, I shall let you know!
