For a description on how to apply tilaka, one should refer to the Hari-bhakti-vilasa (4.66-98). It is stated in Padma Purana, Uttara-khanda: “A practitioner should decorate his body with twelve marks while chanting the names of the Lord such as Keshava.” The process for decorating the twelve parts of the body with the twelve tilaka marks is as follows:
lalate keshavam dhyayen narayanam athodare
vakshah-sthale madhavam tu govindam kantha-kupake
vishnum ca dakshine kukshau bahau ca madhusudanam
trivikramam kandhare tu vamanam vama-parshvake
shridharam vama-bahau tu hrishikesham tu kandhare
prishthe ca padmanabham ca katyam damodaram nyaset
tat prakshalena-toyan tu vasudevaya murdhani
urdhva-pundram lalate tu sarvesham prathamam smritam
such a long mantra, I´ll give you a hint how to learn it:
1. write the mantra down clearly and stick it in the wall just by the tilak. 2. every day read it while applying tilak, do not try to learn it, just say it aloud. 3. in a few weeks you will not need the paper and will know it by heart.
Note: Acc to Vasudeva Upanisad this is how grhasthas (5B) should do it while brahmacaris apply tilak only to forehead, chest, neck and shoulders (5,6). Sannyasis apply it to head, forehead and chest, but with their forefinger (7). 'A paramahamsa should say the sacred syllable Om and place Vaisnava tilaka on his forehead.' (10)
(This numbering is from a V.Up. edition probably translated by Kusakratha P. I've seen another shorter version (1-11 in Kusakratha's edition which has 28 texts) without openly Vaishnava teachings, probably censored out by advaitists.)
