There are some recommended prayers from the book Deity Worship Manual. It is important to water the Tulsi plant regularly. Then carefully pick some leaves and offer for worship to deity of Lord Krsna, or other deities of Jagannath or Panch Tattva. You can also pour water with cow urine (gomutra) on the Tulsi plant. This will help her stay without diseases.
om vrndayai tulasi-devyai priyayai kesavasya ca krsna-bhakti-prade devi satyavatyai namo namah
"I offer my repeated obeisances unto Vrnda, Srimati Tulasi-devi, who is very dear to Lord Kesava. O goddess, you bestow devotional service to Krsna and you possess the highest truth"
yani kani ca papani bhrama-hatyadikani ca tani tani pranasyanti pradaksinah pade pade
"When a person circumambulates Srimati Tulasi-devi, all the sins he may have committed are destroyed at every step, even the sin of killing a brahmana"
nirmita tvam pura devair arcita tvam surasuraih tulasi hara me vidyam pujam grhna namo stu te
"O Srimati Tulasi-devi, you were previously created by the demigods and worshiped by both them and the demons. O Srimati Tulasi-devi, kindly take away my ignorance and accept my worship. I offer my humble obeisances again and again."
om govinda-vallabham devim bhakta-caitanya-karinim snapayami jagad-dhatrim krsna-bhakti-pradayinim
"I am bathing goddess Tulasi-devi, who is very dear to Govinda, who is the mother of the Universe, who gives life to all the devotees, and who bestows devotion to Lord Krsna"
maha-prasada-janani sarva-saubhagya-vardhini adhi-vyadhi-hare nityam Tulasi tvam namo stu te
"O Srimati Tulasi-devi, I offer my repeated obeisances unto you, the mother of maha=prasada. You increase everyone's good fortune and remove all diseases and anxieties"
Look up lectures by Bhakti Visrambha Madhava Maharaj. He is a very devout servant of Tulasi Devi. He has many nice lectures and talks about how best to serve and take care of her. Also on his sight there is a lot of helpful info
Replies
Hare Krsna,
There are some recommended prayers from the book Deity Worship Manual.
It is important to water the Tulsi plant regularly.
Then carefully pick some leaves and offer for worship to deity of Lord
Krsna, or other deities of Jagannath or Panch Tattva.
You can also pour water with cow urine (gomutra) on the Tulsi plant.
This will help her stay without diseases.
om vrndayai tulasi-devyai priyayai kesavasya ca
krsna-bhakti-prade devi satyavatyai namo namah
"I offer my repeated obeisances unto Vrnda, Srimati Tulasi-devi,
who is very dear to Lord Kesava. O goddess, you bestow devotional
service to Krsna and you possess the highest truth"
yani kani ca papani bhrama-hatyadikani ca
tani tani pranasyanti pradaksinah pade pade
"When a person circumambulates Srimati Tulasi-devi, all the sins
he may have committed are destroyed at every step, even the sin of killing
a brahmana"
nirmita tvam pura devair arcita tvam surasuraih
tulasi hara me vidyam pujam grhna namo stu te
"O Srimati Tulasi-devi, you were previously created by the demigods and worshiped
by both them and the demons. O Srimati Tulasi-devi, kindly take away my ignorance
and accept my worship. I offer my humble obeisances again and again."
om govinda-vallabham devim bhakta-caitanya-karinim
snapayami jagad-dhatrim krsna-bhakti-pradayinim
"I am bathing goddess Tulasi-devi, who is very dear to Govinda, who is the mother of
the Universe, who gives life to all the devotees, and who bestows devotion to
Lord Krsna"
maha-prasada-janani sarva-saubhagya-vardhini adhi-vyadhi-hare nityam Tulasi tvam
namo stu te
"O Srimati Tulasi-devi, I offer my repeated obeisances unto you, the mother of
maha=prasada. You increase everyone's good fortune and remove all diseases and anxieties"
Hare Krishna Hare Rama!
Jai Nimai-Nitai!