Namaskaar all,
A Graha in combustion can be likened to someone undergoing a purificatory process. This is to make the qualities of the Graha more purer. It is like being melted and removing of the impurities to make it more Pure. Hence a Graha in combustion is not comfortable and it gives issues for the native to deal with. Like for example Budha may give issues relating to speech, it makes the native somewhat harsh in speech. Shukra's combustion is like the burning of Kaamadeva (eros in Hindu mythology) by Shiva's third eye. Mangal will give temper issues. Guru is said to give issues relating to learning, it is said to be like melting Gold to make it purer. Shani's combustion is not good for Father - child relationship.
There is much more to this.

RishiRahul and vivek.

A Graha which is approaching the same longitude of Surya, meaning it is in the first leg of its combustion will give the burning effect and this tends to be harsh.
Whereas a Graha already past the conjunction with Surya and moving away will give the beneficial results of spiritual renewal and and material benefits. This shows that the person is trying to overcome the evil effects of the combustion.

Surya is the centre of this phenomenon and hence a great deal of importance is given to the Raashi it is placed. Surya is the overlord of the Raashis and he takes 12 forms in the 12 Raashis. These forms are called the Dwaadasha Aaditya.
A Grahas conjunction (combustion) with Surya will be colored by the particular Aaditya of the Sign.

The Aadityaas of the 12 Raashis are:
Mesha: Dhaataa
Vrishabha:Aryama
Mithuna:Mitra
Karka:Aruna
Simha:Indra
Kanyaa:Vivasvan
Tula:Poosha
Vrischika:Parjanya  
Dhanu:Anshumaan
Makara:Bhaga
Kumbha:Tvasttaa
Meena:Vishnu

RishiRahul and vivek.

The following info on the 12 Aadityas are from Pt. Sanjay Rath ji's article in the Magazine- Jyotish Digest.
1.Dhata (Also called Savitur) - Shows the power of creation which comes from words. It is the Omkaar.
A strong desire to create the perfect world.

2.Aryamaana - Generosity and nobility. He is the greatest blesseras he really knows to bless.

3.Mitra - Shows chivalry, constancy and friendship. The name itself suggests that friendship becomes important to the person. You will find these people in  espousing vegetarianism, they want to get rid of cruelty of any kind so, the peta, Human rights social causes will get them involved.

4.Aruna (Varuna) - Power of punishment and blessings too. does not tolerate breaking of social and personal laws.

5.Indra (Sakra) - Ruling power that is a result of knowledge and courage.

6.Vivasvaan - power of service and purity. The tilling of soil and the growing of food.

7.Pusaan - The power of change, questions and their intercourse leading to prosperity.

8.Parjanya - Power of transformation and skills in rituals (secret). Sometimes very radical ways may be adopted to bring about the desired transformation by these people.

9.Amsa (Ansumaan)- Power of Justice, fairness and sharing.

10.Bhaaga - Power of labour giving due earnings.

11.Tvastaa - power of skill in work and new innovations leading to higher gains.

12.Vishnu - power of renunciation leading to truth and universal laws.

Pundit ji has tried to put the qualities in a nutshell, to know more on the Aadityas do read up in the various scriptures, of which at present Google is the one most widely read.

RishiRahul and vivek.