How to make happy?

I always have a problem with unhappiness and therefore cannot build a lot of cities. Any good strategy for getting a happy population from the beginning even with an expansionistic strategy?

 

You could try a tradition 4 cities opening. Try to get as construction as fast as you can then build colusseums in your core 4 cities. This would allow you to expand on a stable basis.

But I usually play tall so I'm not sure if that's the best tactic.

Here's a guide on the Tradition 4 cities opening : http://forums.civfanatics.com/showthread.php?t=468487

 

Religion religion religion... several happiness bonuses available there. Make use of the mercantile city states as well.

 

Easiest way is religion. If you beeline certain techs you'll be able to select your choice of religious benefits. Also, consider building Stonehenge... it alone will allow you to forego making shrines in all your cities (or do both for really fast generation). Make sure and get your 2nd great prophet to enhance your religion before you spend faith on other stuff.

Second is luxury resources... don't settle where you don't have at least one resource. Stay friendly with as many other civs as possible, and trade out resources. (And staying friendly can be difficult... you can't backstab, you can't eliminate other civs, you can't take city states, etc.)

Third are buildings such as colosseum, theatre and stadium. But those generally are spread out along the tech tree.

Fourth are social policies... but they are few and far between (as far as getting happiness goes).

Fifth are mercantile city states, as Dr. D said.

Sixth are some wonders.

 

Your other problem may be that you are building too many cities too early. Unlike previous Civs, you can't just spawn cities nonstop.

Your first city usually starts out with 2 luxury resources. Depending on what difficulty level you are playing, you can build a second city before you have improved any luxuries. But that's the limit until you have luxuries.

Make sure you build that second city in range of at least one new resource if you can. That'll allow you to build more cities quickly.

Go for the techs required to improve the luxuries as soon as you can. Once you have the techs around your capital improved, you can build a third city. Further cities will require more luxuries and/or following what Wodan said.