(1) Re-aligning sleep pattern
In addition to Ofri Raviv's answer (get sunlight), I would like to stress that the only way to re-align your sleep pattern is to get up at the time you want to get up, and keep getting up for as long as it takes for your pattern to re-align, no matter how tired you are. Because, as soon as you give in and sleep longer, you re-inforce the "late" pattern you want to overcome. You will be tired for a day or two, because you didn't manage to get to bed in time, but this tiredness will enable you to go to bed earlier on the following evenings. All you have to do it go to bed when you feel sleepy.
Tiredness is a great help in building a new sleep routine, and sleep restriction (so you are tired enough to actually sleep) is a regular part in many behavioral therapies of sleep disorder. Because one fundamental problem in sleep disorders is that people spend to much sleepless time in bed, causing them to want to sleep in in the morning. When you go to bed, you want to be tired enough to fall asleep immediately, so that you get at least five hours of undisturbed sleep. But always keep your wake-up time, and work at the go-to-bed time end of your sleep cycle.
Also, avoid computer and television monitors in the evening, because they have the same effect as sunlight and will tell your body that it is still day and you should be active. So, get sun (and computer screens) in the morning, as Ofri Raviv wrote, and avoid them in the afternoon and especially evening. Sleep with the blinds open, so the morning sunlight helps wake you. An open window and fresh air will also help you feel less groggy in the morning.
(2) Maintaining a regular sleep pattern
The answer is already given in the question. As simple and tautological as it may seem, a regular sleep pattern can best be maintained by maintaining a regular sleep pattern. Behavioral therapy for children and adults with sleep disorders includes one fundamental rule, which is to go to sleep and wake up at the same time every day. No surprises there.
So, the best idea would be to not party so late that you need to sleep more than two or three hours longer than regular, and not for more than one night per week. If you need to party, you better don't go to bed at all or get up at your regular time, no matter how short your sleep was, and got to bed at your regular time (or a bit earlier) on the following evening. This will minimize the disruption. The important part is that you get up regularly on the next day.
Witnessing sleep therapies in our local psychotherapeutic day clinic.
Short introduction to behavioral sleep therapy at Wikipedia: