A good complement to strace is ltrace(1):

  ltrace is a program that simply runs the specified command until it exits. 
  It intercepts and records the dynamic library calls which are called by the executed process and the signals which are received by that process. 
  It can also intercept and print the system calls executed by the program.

Also noteworthy is that you can simply press s key in htop to immediately attach a process and inspect it, which was handy many times for me.