Friends:

What 4 Objects of Thinking are always Advantageous?

Once in Savatthi the Blessed Buddha said this:
Bhikkhus do not accept to think any evil disadvantageous thought such as:
1: Thoughts mixed with Sense-Desire...
2: Thoughts mixed with Ill Will or Anger...
3: Thoughts mixed with Harm & Violence...
Since all these thoughts are irrelevant and even detrimental to the basics of
the Noble life & they furthermore do neither induce revulsion, nor disillusion,
nor ceasing, nor Peace, nor any true knowledge of Enlightenment or Nibbāna!
When you think, Bhikkhus, you should only think thoughts like these:
1: This is Suffering;
2: This is the Cause of Suffering;
3: This is the End of Suffering;
4: This is the Way leading to the End of Suffering...
Why so?
Such thoughts are of prime relevance and highly advantageous to the basics of
the Noble life & they furthermore gradually induce both revulsion, detachment,
stilling, Peace, and direct knowledge of Enlightenment & Nibbāna. Therefore,
Bhikkhus, an effort should be made much of so to completely understand:
This is Suffering; This is the Cause of Suffering; This is the End of Suffering;
This is the Way leading to the End of Suffering... An effort should be made to
understand, comprehend, penetrate, recognize & realize these 4 Noble Truths!

                                 

Comments:
Keep mind focused on these 4 facts whenever it strays into fun, wrath or ill...
 

More on these 4 Noble Truths (Cattari Ariya Saccani):
http://www.accesstoinsight.org/lib/study/truths.html
http://What-Buddha-Said.net/library/DPPN/wtb/s_t/sacca.htm
http://www.accesstoinsight.org/ptf/dhamma/sacca/index.html
http://What-Buddha-Said.net/drops/II/The_4_Noble_Truths.htm
http://www.accesstoinsight.org/lib/authors/thanissaro/wings/part3.html#part3-h-1
http://What-Buddha-Said.net/drops/II/The_1st_Noble_Truth_on_Suffering.htm
http://What-Buddha-Said.net/drops/II/The_2nd_Noble_Truth_on_The_Cause_of_Suffering.htm
http://What-Buddha-Said.net/drops/II/The_3rd_Noble_Truth_on_The_Ceasing_of_Suffering.htm
http://What-Buddha-Said.net/drops/II/The_4th_Noble_Truth_on_The_Way_to_End_Suffering.htm

Source (edited extract):
The Grouped Sayings of the Buddha. Samyutta Nikāya. [V:417-8]
section 56: Saccasamyutta. Thread 7: Thoughts...

Focused Thinking!