smiling is the best reaction in all situations

the road of life is like a large river,because of the power of the currents,river courses appear unexpectedly where there is no flowing water

This is okay. If you wanted to sound more like an English speaker You might say...

A smile is the best way to respond in all situations. 

Life is like a great big river. There are powerful currents and river courses can unexpectantly occur where there was previously no water at all. 

In North America we often use 'great big' in spoken language  For example, 'there was a great big bear chasing us, a great big hole in his pants, a great big crowd, a great big stain on her shirt. This is just a common way that we emphasize how big something is and sounds more like street talk and less formal than 'large'. You can use the words huge, really big, monstrous and massive and they mean much the same...there was a huge - really big - great big - massive- montrous spider in the sink. 

Have fun!