There are some quite detailed meditation instructions in the 5th century AD Tirumantiram by Saint Tirumular. The Tirumantiram is introduced as such on Wikipedia:
The Thirumantiram is a Tamil poetic work written in the fifth century by Thirumular and is the tenth of the twelve volumes of the Tirumurai, the key texts of Shaiva Siddhanta and the first known Tamil work to use the term. The Tirumantiram is the earliest known exposition of the Shaiva Agamas in Tamil. It consists of over three thousand verses dealing with various aspects of spirituality, ethics and praise of Shiva. […]
You can download an English translation here.
Most of the passages dealing with meditation occur in the 3rd Tantra, verses 549 to 631 (slide 131 to 150). Here are just a few examples to give an idea of its content:
On virtue:
554: Ways of Niyama
He does not kill, he does not lie, he does not steal;
Of marked virtues is he; good, meek and just;
He shares his joys, he knows no blemish
Neither drinks nor lusts
–This the man who in Niyama’s ways stands.
On asanas (here they are sitting postures only):
559: Padmasana–Lotus Posture
Sit cross-legged with soles of feet upturned
Close draw the feet on thighs opposite,
Stretch then the hands afore on feet
That Padmasana is, famed far on earth.
On breath meditation (many passages, here just a couple):
567: Breath Control Yields Life Nectar
Let Prana merge in Mind
And together the two be stilled
Then no more shall birth and death be;
Therefore, learn to direct breath
In streams alternating left and right
And in silentness chant “Aum”
574: How to Practise Pranayama
Inhale deep and steady,
That prana fills the nadis ten;
Exhale slow
That the body does not stir;
Retain prana breath
And downward move Apana breath
Thus sit erect and vanquish Death.
On guarding the senses:
578: Blessings of Mind Withdrawal
Step by step, practise mind’s withdrawal
And look inward;
One by one many the good you see within;
And may you then meet the Lord,
Now and here below
Whom the ancient Vedas still searches
Everywhere.
There is also the turtle simile:
133: Senses Controlled, They Saw This World and Next
Who there be who, like our Lord, distinct know
The great and the small, the difficult and the facile?
They, unto tortoise, drawing in senses five under the shell,
They heard and saw This and Next, all impurities dispelled.
On light and divine bliss while meditating:
582: When Light Appears
If thus meditating,
Luminescence you glimpse at the Eye-brow centre
Know you are destined for bliss unalloyed;
If at the Throat’s Center
Lunar light you behold,
Then will your body,
In divine joy intoxicated be.
On equanimity:
629: Tranquility in Samadhi
Samadhi attained, Siva is attained;
Sakti too will be caught in its fold;
Distracting passions will be dispelled;
In equanimity perfect,
Like unto a balance
Will be the mind
All this, for those who in Samadhi sleep.
Indeed!:
574: How to Practise Pranayama
Inhale deep and steady,
That prana fills the nadis ten;
Exhale slow
That the body does not stir;
Retain prana breath
And downward move Apana breath
Thus sit erect and vanquish Death.
[…]
595: Mind Control Through Breath Control
[…]
They who control breath in measure ordained,
Will sure imprison mind-monkey
Within the body-fortress.
596: Make the Body Immortal
Also @frankk, I recall a post you made about the siddhis, they are mentionned in this text at verses 640 (slide 152) to 711, in case you are interested by how this text treat them…
668: The Eight Siddhis Enumerated
To become tiny as the atom within atom (Anima)
To become big in unshakeable proportions (Mahima)
To become light as vapour in levitation (Lahima)
To enter into other bodies in transmigration (Prapt)
To be in all things, omni-pervasive (Prakamya)
To be lord of all creation in omnipotence (Isavatam)
To be everywhere in omnipresence (Vasitvam)
–These eight are the Siddhis Great.
[…]
705: Conduct of Aspirant For Yoga Samadhi
To give up thoughts of women
To think no more of kith and kin
To be meek in learning
To abound in jnana
To be sparing of speech
To listen to deeds of Siddhi
To sit unruffled
–These the ways of the aspirant of yoga samadhi.