Powerful ways to invoke Lord Krishna:-
Mantras when chanted continuously, in whatever condition (except for certain unclean and prohibited situations ),time or place will yield maximum results. The mantra has to get into the system of the practitioner, it has to flow along with every drop of blood within the body and every breath taken inside, that way the mantra becomes part and parcel of oneself. Normally such a recitation of a mantra would yield results within just one week or maximum ten days.
Krishna mantras are extremely powerful, and these are a few of them:-
1)To experience Lord Krishna in one's heart and to literally feel His presence in day to day life (even today), one has to read atleast one page of Srimad Bhagavatham everyday.It is better to maintain a particular timing for the parayanam.
2)In extreme difficulties,trials and tribulations the following sloka (recited continuously within oneself) will yield immediate results :-
"Hey Krishna!Dwaarakaavaasin! Kwaasi Yaadava Nandana! Apadbhihi Paribhoothaamaam,Thraayashvaashu Janaardhana!"
3) To attract social gatherings, group of friends or relatives or to allure public,"Om Kleem Krishnaaya Govindaaya Gopeejanavallabhaaya Swaaha!"
4)To get the vision of Lord Krishna in one's dreams in whatever relationship one seeks with Him, one must do the 'anusandhanam' -repitition of the 6th sloka of second chapter (Sankhya Yoga or the yoga of Knowledge) along with every sloka of the eleventh chapter (The yoga of the vision of the Universal Form) of the Bhagavad Gita.
The sixth sloka of the second chapter :-
"Kaarpanyadoshopahatasvabhaavaha Pruchchaamithvaam Dharmasammoodhachethaaha,Yachchreyah Syaannischitham broohi thanme
Shishyastheham shaadhi maam thvaam prapannam!"
The above prayer should be done everyday for 4o days,especially on Ekadasi,Pournami,Ashtami ,Dashami and Rohini nakshatram days to attain the vision of Lord Krishna in dreams.
5) To bring back or infuse love into a relationship,"Om Radhakrishnaya Namaha".
6)When Jupiter (Guru) is malefic or misplaced in one's horoscope; during Guru Mahadasa or during malefic transit of Guru in the 1st, 3rd, 4th, 6th, 8th,10th, and 12th houses from moon in their natal charts, one should chant Sri Krishnaashtakam every morning and especially on Thursdays.By reciting the ashtakam, the malefic results due to Jupiter would be nullified.
Vasudevasutham Devam Kamsa Chanooramardhanam
Devakee Paramaanandam Krishnam Vande Jagathgurum!
Athasee Pushpasamkaasham Haara Noopura Shobhitham
Rathnakankanakeyooram Krishnam Vande Jagathgurum!
Kutilaalaka Samyuktham Poornachandra Nibhaananam
Vilasathkundaladharam Devam Krishnam Vande Jagathgurum!
Mandaaragandha Samyuktham Chaaruhaasam Chathurbhujam
Bahirpinchaavachoodaangam Krishnam Vande Jagathgurum!
Uthphulla- Padma-Pathraaksham Neela -Jeemootha-Sannibham
Yaadavaanaam Shirorathnam Krishnam Vande Jagathgurum!
Rukminee- Kelisamyuktham Peethaambaram Sushobhitham
Avaaptha Thulaseegandham Krishnam Vande Jagathgurum!
Gopikaanaam Kuchadwandwa Kumkumaankitha Vakshasam
Sreeniketham Maheshvaasam Krishnam Vande Jagathgurum!
Sreevathsaankam Mahoraskam Vanamaalaaviraajitham
Shankhachakradharam Devam Krishnam vande Jagathgurum!
Krishnaashtakamidam Punyam Praatharutdhaaya Yah Pateth
Kotijanmakrutham Paapam Smarena Vinashyathi!
7) For people who are suffering from malefic placement of Rahu,or Rahu Mahadasa or Kalasarpa Dosham in the horoscope, the parayanam of Narayaneeyam and especially the chapter and slokas of Lord krishna's Kaliyamardhanam would yield immediate results.
8)"Simhaha Prasenam Simho Jaambavathaa Hathaha Sukumaaraka Maarothee,Thava Hyesha Syamanthakaha!"
The above sloka is sung as a lullaby by the daughter of Jambavatha to the little son of Jambavatha,while putting him to sleep.By reciting this sloka, one would regain one's lost reputation or clear his/her name of blemish or an unwarranted blame. This sloka encompasses the entire Syamanthakamani episode of Sri Krishna.This sloka is recommended by Paramacharya in His Deivaththin Kural,4th Volume for everybody to recite in their daily prayers to attain their wishes and to lead a blemishless life.
9)For girls who wish to get married,especially for girls whose lagna and Rahu are conjoined or whose Mars is conjoined with kethu in their horoscopes,the 4th sloka from the 21st Canto of Narayaneeyam would yield results:-
"Varshe Pratheechi Lalithaathmani Kethumaale
Leelaavisesha Lalithasmitha Shobhanaangam
Lakshmyaa Prajaapathisuthaischa Nishevyamaanam
Thasyaahaa Priyaaya Dhruthakaamathanum Bhaje Thvaam!"
10)Daily rendition of Sri Parthasarathy krithi in Suddha Dhanyasi by Sri Muthuswami Dikshithar (set to rupaka thalam) is meant to invoke Lord Krishna when the practitioner is in crisis and needs the guidance and direction from Lord Krishna as Sarathy, to take control of the practitioner's life into His hands to lead him/her.
11) Innumerable krithis on Lord Krishna composed by Sri Dikshithar (the rare Bala Krishnam in Gopika Vasantham ), Sri Narayana Theertha, Sri Purandaradasa, Sri Oothukadu Venkata Subbaiyer, Meerabai, Ambujam Krishna etc. and many other composers are outpourings of love for Lord Krishna and rendering them as prayers is as effective as slokas and mantras due to the blessings and vibrations of the saintly composers.
12)To invoke Nayika Bhavam in oneself towards Lord Sri Krishna, one must render all the ashtapadis of Sri Jayadeva (Gita Govindam) and the raga Brindavani and Abheri which are dear to Radha.
13)Empathizing with Radha through slokas and songs composed on Her would endear the practitioner to Lord Krishna!