How to do a long meditation of "death contemplation"? because just thinking about it for a short time didnt have any effect on me   - how should i do a long death contemplation meditation ? like half hour or an hour  ? 

should i repeat a mantra over and over again ?    

And what to do when there are disturbances - should i focus on the words more strongly ?  where my attention should be ?  

(doing death contemplation to gain a sense of urgency - chanda)
In the Tibetan Geluk tradition, contemplation of death would usually involve the two:


Analytical meditation on death
Placement meditation on a specific mind induced by analytical meditation


A beginner would start with 24 minutes meditation sessions. The point is to do it every day.

For instance, by engaging in analytical meditation on "death is certain, but its time is most uncertain, and at death only karma will follow", a mind of non-attachment to your goods will arise, or a mind of non-anger towards your so called-enemies will arise, or a mind of loving kindness for friends you are presently angry with will arise, or a mind wishing to practice dharma and a sense of urgency will arise.

When this or that mind arises, we are advised to take it to mind, concentrate on it, stay with it without analyzing anymore. This is to dwell in these "places" and familiarizing with it. Every time you dwell on non-attachment, you make it easier to dwell on it again. Moreover, every time you manage to make a mind of non-attachment arise, finding your way there (so to speak) becomes easier.

When you loose your object of concentration (be it a mind of love, non-attachment, urgency, etc) you engage in analysis again for it to arise again. The purpose is to find your way to these "places" and dwell on them again. We are very skilled in doing so with anger, feeding it, finding reasons to be unhappy and angry, and staying with it.

In the Geluk tradition, this type of meditation (alternating analytical and placement) are laid out in the Lam Rim (i.e. Stages of the Path). Venerable Karin Valham compiled an outline of it: Lam.Rim Outlines &ndash; Beginners' Meditation Guide. Whether you want to meditate on impermanence and death, or precious human rebirth, or suffering, etc. this is just food for thought.