key ignition refusing turning sometime... until i use the spare key and try harder before turning, please what can cause it?

Use the key that works best , if you have a key made go to a locksmith not a grocery store , the lock is probably worn and will need to be replaced , don't force it that will make it worse get a feel for the position the likes , I saved $$ getting a lock set from a smith rather than the dealer , that was a ford a foreign car might not be available , the lock smith may have some suggestions for you , he doesn't work on commission