I mean when you’re by yourself, in your room or house etc. and not in a church. 

An act of adoration. 

Does it suffice to say it mentally, “Most Holy Trinity, I adore Thee”.

In what does adoration consist?

Just saying the Holy Name of Jesus while bowing your a few times throughout the day is a prayer, an act of adoration. After a while that morphs into "May the holy name of Jesus be forever blessed and praised" and sometimes after a while of that it morphs into....

One of the things I do is when no one else is around is when I walk past the Sacred Heart picture in my hallway, I strike my breast and say to myself "most sacred heart of Jesus have mercy on me." I do something similar with the other pictures and statues at my house. They are there for reminders after all. 

One thing that's common in Ireland (may not work in other countries) is to cross oneself whenever one passes a Marian grotto, or a statue of any holy figure.

Another thing I like to do is to hold a rosary, even when I'm not praying the rosary, and then to kiss the cross upon it.

don't be so legalistic in your approach 

prayer books, liturgy, and the saints are good examples to follow but every act of adoration doesn't have to be exactly like theirs

you can add your own

It depends upon the situation. If I drive past a Church with a beautiful statue of the Sacred Heart of Jesus, I’m not going to come to a screeching halt, run from my car, and prostrate myself in full view.
If I’m by myself and I’m going to pray in my home, I might prostrate myself. 
Generally, I make the Sign of the Cross, often, even in public. One may adore in one’s heart only.  If, by public actions or words, others will mock or curse God, then it’s best to offer silent  adoration. 
This is even cultural. I grew up in NYC when there were still very ethnic parishes. If you went to Mass in the Italian parish, it wasn’t unusual to see people kissing statues or prostrating themselves and praising aloud. The same behavior in my mostly Irish parish would have been considered highly improper and undignified. 
Personally, I’m not a person given to public displays of worship, adoration, or emotion. I don’t judge those who aren’t like me. I’ve been around enough to realize there are all kinds of Catholics, and I’m not referring here to being “ecuмenical” in the Vat. 2 sense of the word.