The best way to create a positive attitude and working environment between coworkers is to simply treat your fellow employees as you wish to be treated. It sounds simple, but is very effective. The relationships that exist at work are no different than any other interpersonal relationship in a person's life at a basic level. They have to be cultivated and actively worked on if they are going to be positive and successful.
While certainly not a comprehensive list, some ways to show a positive attitude towards your fellow employees could include: smiling and using positive body language around them, asking about their day and personal life, showing interest in the things that are important to them, inviting them to lunch or maybe a social gathering after work if appropriate, offering to help them if they obviously need assistance or simply looking for opportunities to be helpful, being slow to anger if someone does something upsetting, having open lines of communication, and trying to view conflicts through their perspective in hopes of understanding the source of their feelings and actions.