Make sure everything compiles cleanly. Use the strict compilation options for extra checking.
make CFLAGS="-ansi -pedantic -Werror -W -Wall -Wtraditional -Wconversion -Wshadow -Wpointer-arith -Wcast-qual -Wcast-align -Wwrite-strings -Wstrict-prototypes -fshort-enums -fno-common -Wmissing-prototypes -Wnested-externs -Dinline= -g -O4"
Also use checkergcc to check for memory problems on the stack and the heap. It's the best memory checking tool. If checkergcc isn't available then Electric Fence will check the heap, which is better than nothing.
Make sure that the library will also compile with C++ compilers (g++). This should not be too much of a problem if you have been writing in ANSI C.