In addition to what @RabbiKaii writes (very good job!), I've found some material in Chassidus.
The Rebbe Rayatz writes in the maamar Basi LeGani (5711, chapter 4):
By contrast, [physical] created beings not only fail to reveal [their] Creator, they actually hide and conceal their source; moreover, they feel that their being derives from themselves, (and only reason dictates that this cannot possibly be so)).
Although this [perception of a physical creation that its being
derives from its own self] is but its own [false] impression,
nevertheless, the very fact that it is able to imagine that it derives
from its own self results from its being rooted in G‑d's Essence — and
His Being derives from His Essence.
The Rebbe in the maamar "Yehudah Atah" (5746, Shabbos Parashas Vayechi, 16 Teves) quotes the Alter Rebbe who says that Yehudah is identified with the quality of bittul. Since it is stated that Yehudah said:
Now will I praise the Lord
In this case, there are two terms that describe Bittul.
"Bittul hayeish" - When serving G-d, have in mind nothing but to bring gratification to the Creator, blessed be He, and not the attainment of [high] levels. See Tzava'at Harivash 47 by the Baal Shem Tov.
"Bittul bemetzius" - "The state in which one’s entire existence is negate" - See: the maamar U’Shavtem Mayim: Sukkos, section 3.
In "Selections from Likkutei Sichos - Bereishit" (Addendum, p. 702), the Gemara in Sukkos 4a is cited. The Gemara discusses that if a person brings straw or earth in order to increase the height of the floor, if the person has the intention to not remove it, e.g. it was placed there to stay there, it is considered bitlo (see Rashi; Makkos 15a where בטלו is discussed).
In "Selections from Likkutei Sichos - Bereishit" (Addendum, p. 702) it goes on to explain that the wording בטלו in the Gemara in Sukkos, is used because if one has the intention to increase the height of the floor of the Sukkah, and not removing it, it is considered not as "stand-alone earth/straw", but part of the Sukkah itself. Just like this is the case with this Gemara in Sukkos, so too it is the case with Bittul in our Divine Service. Bittul means that we are meant to see ourselves not as an independent entity, but that we are meant to see ourselves as servants of Hashem, and that we recognise that purpose.
I recommend reading "Selections from Likkutei Sichos - Bereishit" (Addendum, p. 702) where the building blocks of Chassidic thought is thouroghly explained. Including the concept of Bittul.
Similary, the Ramak, Rav Moshe Kordovero, writes in his Or Neerav:
[...] that the Creator, may He be blessed, [is found] in all things in actuality, while all things are [found] in Him in potential. He is the beginning and cause of all things. (emphasis mine)
You'll need to have bittul, e.g. realise that you are not an independent entity, but rather, even you are found in Him, since He is the cause of everything.