Answer
God-realization occurs in many ways; there are multiple paths to it. Primarily, there are two kinds of approaches.
The Bhagavad Gita states that some people worship the Lord with a sense of separateness, while others worship with a sense of oneness. Those who worship the Lord with a sense of oneness believe that there is no need to "attain" the Lord — we ourselves are the Lord; our Atman itself is the Lord. One simply needs to know this and experience it directly. The moment this direct, immediate experience (aparoksha anubhuti) dawns, God-realization is attained. Dhyana Yogis (meditators) and Jnana Yogis (seekers of knowledge) "attain" the Lord in this manner.
For Dhyana Yoga, there is Maharishi Patanjali's Yoga Sutra, which one should study to acquire knowledge of this path. Thereafter, one should practice sadhana under the guidance of an accomplished Dhyana Yogi. The second path is that of Jnana Yoga, which begins with the study of scriptures. Then there is continuous reflection (chintan), contemplation (manan), and deep meditative absorption (nididhyasana) upon the teachings of the scriptures. This process continues for decades. Then, one day, suddenly, the practitioner begins to have a direct, divine experience of the knowledge he has read in the scriptures — and then it is said that he has "attained" the Lord.
Those who worship the Lord with a sense of separateness — such as Bhakti Yogis (devotees) — hold the view that the Lord is the whole (Amshi) and we are the parts (Amsha). We cannot equal the whole. They do not speak of "self-realization" or Atma-bodha; rather, they wish to go to Vaikuntha and, while maintaining their separate identity, dwell in the Lord's abode and enjoy His divine bliss for eternity. When they finally reach Vaikuntha, God-realization is attained. Even before reaching Vaikuntha, there are many stages — such as having a vision (darshana) of the Lord and conversing with Him. Those who have advanced considerably in Bhakti Yoga often receive darshana of the Lord and converse with Him.
Karma Yogis also attain the Lord by performing all their actions with detachment and by offering them to the Lord. In this way, they remain constantly absorbed in the Lord, and according to their preference, they either attain Brahma-nirvana (merging into the formless Brahman), or, if they are also devotees, they reach Vaikuntha.
Whether one is a devotee, a Jnana Yogi, a Dhyana Yogi, or a Karma Yogi — if at the time of death one leaves the body while remembering the Lord, one reaches the Lord's abode and God-realization is attained. However, the Lord does not come to mind at the time of death easily — He is remembered only when one has cultivated the habit of constant remembrance over a long period and one's mind naturally dwells in Him. Yet, if at the very moment of death one takes the Lord's name and remembers Him with genuine devotion, liberation is attained and the person reaches the Lord's abode.