We've all heard that attitude counts at work, but what does that mean? In general, it means to be positive and enthusiastic, even when things go wrong. It's a good idea not to criticize the competition: yours, your employer's, or the client's with whom you're speaking. In fact, it's a great idea never to criticize anyone (or talk about them at all) within earshot of a customer or colleague, unless you know, without-a-doubt, that your conversation will be kept private.
If you do have a complaint or concern, instead arrange to meet privately with that person or group to share your concerns. And, when presenting those issues (particularly to your supervisor), don't just share the issue and expect the other person/group to fix it. Rather, share the issue and some potential solutions and then ask the person or group for input (or a recommendation, if appropriate). Remember, always praise 'down' (to subordinates), in order to maintain good morale, and protest 'up' (to supervisors) in order to help solve problems. Your words and actions to colleagues and subordinates in particular should be as positive as possible.
Some work environments are more intimate than others, so it's important to gauge a new workplace for awhile before jumping in and sharing all of your personal problems or stories. In some workplaces, the lines between personal and professional are very clear. Leave personal problems at home. In others, however, something more akin to friendships develop and the lines get a bit more blurry. Take some time to be an observer and ensure it's acceptable before letting your own lines get blurred!