Also wanted to add that specific smells ime can lead me into a zone of specific memory/ies [or no-memory] prior to smoking . Smells that have been deeply ingrained due to past experiences with these specific smells [i.e: a certain type of incense or candle]. That can help zone me in/lock me into what is happening and everything else drops away.
Another thing I would use often is some sort of rhythmic, repetitive music [something preferably uplifting, melodic, or even something downtempo and soft yet repetitive]. I agree with the camp that music can be a hindrance, depending on the situation, though it's seemed to really help for me leading up to the experience - and in specific situations has driven the experience [but this is going outside the scope of this thread I think].
As I'm sitting there, not really thinking of anything, slightly nervous though not really thinking on 'oh my god im about to do this' I'll usually start the song, and I start to zone into the song, the rhythm, the lyrics[?], just totally get into the music, lose all awareness or worry, guess you could equate it to psyching yourself out in a sense though I think it's a bit more than that. It definitely has became a sort of meditation for me numerous times right up until smoking.
** Though after a certain point the music becomes a faint whisper, barely perceptible, or completely inaudible to the point of not even being remotely recognizable [during the peak of the onset of the experience, so it typically only helps me up until a point, then it's all out the window
].
Hope this helps 