Classification of Houses

Trikonas - 1, 5, 9:
Trikonas (and their lords) are the most auspicious houses in the chart. The trikonas are dharmasthanas. They bring spirituality, knowledge, goodness, generosity and well-being if they are well placed and unafflicted.

Kendras - 1, 4, 7, 10:
Kendras (and their lords) are considered auspicious as they represent some of the most important and fundamental areas of our lives - body and innate nature, home and mother, marriage and relationships, our position in society (profession/status) and so forth..

Trikasthanas - 6, 8, 12:
Are considered to be the three evil houses of suffering (dusthanas). These houses and their lords bring difficulties, suffering, loss, anxieties, worries, obstacles, disease, confinement/isolation, impediments, enemies, lawsuits, accidents, injuries, surgeries, and death like experiences into our lives.

Trishadayas - 3, 6, 11:
Are considered malefic. BPHS Ch.34: 3-4, says; "Any planet owning the 3rd, 6th, or 11th will give evil effects." The malefic quality of the 11th house (most powerful trishadya) is greed as it is one of the three kama or desire houses. The Bhagavad Gita states:

"Tri-vidham narakasyedam dvaram nasanam atmanah
kamah, krodhas tatha lobhas tasmad etat trayam tyajet."

Which translates as:
"Desire, anger and greed - the triple gate of hell bring about the
ruination of the soul. Therefore one should avoid all these three."
Ch.16 verse 21.

Trishadaya lords can signify difficulty and/or disease, especially when aspecting vulnerable bhavas/grahas.

Upachaya Houses - 3, 6, 10, 11:
The upachaya houses are the best house placements for the natural malefic planets. They are also considered "increasing" or "growing" houses because they are said to improve with time as the person gets older.

Marakasthanas - 2, 7:
Are marakas (killers) due to their owning 12th from 3 and 8 (the houses of longevity). Planets occupying or owning these houses can cause death during their dasas. If they operate before the time of death is promised, they can bring death like suffering, disturbance of the health etc..

Bhava/Rashi
Element
*Dosha
Quality
Classification
1. Aries
Fire
Pitta
Cardinal/Chara (kendra)
Kendra/Trikona (dharma)
2. Taurus
Earth
Vata
Fixed/Sthira (panapara)
Marakasthana (artha)
3. Gemini
Air
Tri-Dosha
Mutable/Dwi-swabhava (apoklima)
Trishadaya/Upachaya (kama)
4. Cancer
Water
Kapha
Cardinal/Chara (kendra)
Kendra (moksha)
5. Leo
Fire
Pitta
Fixed/Sthira (panapara)
Trikona (dharma)
6. Virgo
Earth
Vata
Mutable/Dwi-swabhava (apoklima)
Trikasthana/Dusthana/Upachaya (artha)
7. Libra
Air
Tri-Dosha
Cardinal/Chara (kendra)
Kendra/Marakasthana (kama)
8. Scorpio
Water
Kapha
Fixed/Sthira (panapara)
Trikasthana/Dusthana (moksha)
9. Sagittarius
Fire
Pitta
Mutable/Dwi-swabhava (apoklima)
Trikona (dharma)
10. Capricorn
Earth
Vata
Cardinal/Chara (kendra)
Kendra/Upachaya (artha)
11. Aquarius
Air
Tri-Dosha
Fixed/Sthira (panapara)
Trishadaya/Upachaya (kama)
12. Pisces
Water
Kapha
Mutable/Dwi-swabhava (apoklima)
Trikasthana/Dusthana (moksha)
Although modern astrology software calculates strengths such as "Sthana Bala" for us, it's beneficial to understand the basic principles of these strengths. For instance, a planet in a kendra (1,4,7,10) gets 60 shashtiamsas whereas a planet in 2nd from a kendra (panapara) gets 30 shashtiamsas and a planet in 12th from a kendra (apoklima) gets only 15 shashtiamsas.
*A Brief Summary of the Doshas:
Pitta - Can be summarised as being rather strong-minded, determined to get things done...reddish/hot.
Vata - Not always good at memorizing things and then remembering them later...thin/cold.
Kapha - Do not (generally) learn as quickly as some but have excellent retention and long memory...plumpish/placid.
More can be seen on the "Medical Astrology" page...

Determination of Malefic/Benefic Status
Except for the luminaries (Sun & Moon) all planets own two houses, i.e. "Own House" and 'Moolatrikona House'. When determing a planet's malefic/benefic status (as per Parashara) the planet's moolatrikona house takes precedence over own house.

BPHS Ch.34:
2-7. NATURE DUE TO LORDSHIPS OF PLANETS:
"Benefics owning angles will not give benefic effects while malefics owning angles will not remain inauspicious. The lord of a trine will give auspicious results. The lord of the ascendant is specially auspicious as the ascendant is an angle as well as trine. The 5th, and 9th houses are especially for wealth while the 7th and 10th are specially for happiness. Any planet owning the 3rd, 6th, or 11th will give evil effects. The effects due to the lords of the 12th, and 8th will depend on their association. In each group, the significance will be in the ascending order. The 8th lord is both inauspicious as he owns the 12th from the 9th. If the lord of the 8th simultaneously owns the 3rd, 7th, or 11th, he will prove specifically harmful while his simultaneous ownership of a trine will bestow auspicious effects. The planet owning a predominant house will stall the effects due to another owning a less significant house and will give his own results. The 8th lordship of the Sun and the Moon is not evil."

Further reading... BPHS Ch.34:19-44