I would echo the advice of the other two answers, but would like to provide specific advice on screws.
I've heard good things about SPAX screws, and they have a guide to pre-drilling sizes here http://www.spax.com/uk/technical-terms/pre-drilling which may be useful.
Personally I've always used Reisser R2 wood screws which come pre-lubricated and I've VERY rarely had problems with the screws breaking or being hard to drive in, even without pre-drilling. I work at a joinery and we make thousands of hardwood windows each year. We've tried other screws as there's always somebody trying to sell their fancy new wood screws with Torx drive and cutting tips, self-countersinking heads etc. but nothing is a patch on the Reisser screws.
If you try these screws and still have trouble, then try pre-drilling. If you still have problems after that then something else we've tried when driving in long (160mm) decking screws is applying some silicone sealant to the screw thread, by dipping the screw into the end of a tube). This lessens the friction and also makes it easier to remove the screws later, if necessary.