If your two doggies are suddenly vying for your attention in more aggressive ways, it might be plain old jealousy. Psychology Today says dogs who see other dogs get rewards they don't get will become jealous and annoyed toward the other dog. So if you're playing favorites and rewarding one dog more than the other, you shouldn't be surprised when the green-eyed monster rears its head.
Give each dog individual attention. That means spending some "alone time" with each pal separately if at all possible. When they're together, make sure both get equal treatment. If one gets a treat, so does the other. One doggie gets kissed or an ear rub, then the other should too. Make space for both or neither on the couch -- if you make some concessions for one dog but not the other, you can expect chaos to ensue.
Honor the "top dog" status, whatever it is. If they came into your household at different times, then usually the first who arrived will be the top dog. However, it's also possible that roles will eventually change. Whether you agree or not with the position, respect it. It means top dog gets his bowl of food or his daily treat first.
Stop fights before they start. Jealousy among dogs can and will lead to fights unless you do something about it. The best option? Let the dogs know you're the boss. This starts with basic commands. For example "sit" before they get their meal, so they show they respect who controls the food. Then when things get rough between them, it's a lot more likely they will listen to you when you say "stop."
Introduce new people gently. For example, if somebody just moved into your house or you recently got married, the dogs might fight over who gets to "own" the new human. To prevent his, make sure the new person takes on the role of leader too. He should follow your lead and use the same commands and training techniques to ensure the dogs respect him as much as they respect you.