If a previous kernel (assuming it is not from the stone age) compiles successfully, does it make sense to assume that old config file if copied to the new kernel, will compile successfully too?What things need to be taken care of?  
Precautions to be taken while make oldconfig
linux;kernel;compiling
Copy the old .config file and then, to know what needs to be taken care of, use make oldconfig. You will be prompted interactively for needed changes in your config file. It's almost safe to answer with the default option to every question. (Usually you don't care about new drivers, and you want to use new features when those are enabled by default).If you skip this configuration update step, things might break.