Many players tend to strongly favor either offense or defense. Even at higher levels, many players are very comfortable attacking, but get uncomfortable and inconsistent when the opponent attacks first. At lower levels, it's often the reverse, where they are most comfortable pushing and blocking, and hoping the opponent misses.
One of the quickest ways to judge a player's potential is to see if they are equally comfortable attacking or defending. This doesn't mean they are equally good at both - especially at higher levels, most are better when attacking. But if a player is equally comfortable attacking or defending, and so proficient at both, he can go a long way.
So, develop a game where, while you might emphasize attacking (though some might emphasize defense), you can do either. It's not just your proficiency - it's also the attitude. If you are comfortable and confident when the opponent attacks first, then under pressure you are likely to handle his shots far better than if you are only comfortable attacking.
Learning to attack is straightforward - work with a coach and practice! Learning to defend is the same - have someone attack while you block (or whatever other defensive shots you choose) until you are so comfortable doing this that, when it's time to do it in a close match, it's second nature.