I hate using the call bell, and avoid it at most costs.  I much prefer to get the attention of crew as they walk by. 
If I finish my drink and want another, I'll usually try and get the attention of crew as they walk by.  If none walk by and I'm in an aisle seat, I will walk to the galley and ask. 
The only time I will really use it is on an overnight flight when the cabin is dark and the crew are not routinely walking by, and I don't feel up to walking to the galley.  (ie if I've taken a sleeping tablet and woken up halfway through needing water).  
If at a window seat and the person next to you is sleeping, that's pretty much a free pass to use the call bell if the staff are not being proactive with service.