In the Vedic religion, Sanatana Dharma popularly known as Hinduism, God or Bhagavan or Isha is beyond all names and forms as well as, in and through every name. Hence, we have the freedom to worship in multiple ways and relate to many forms. There is an amazing variety in the way Ishvara is invoked as different deities. Even each deity like Shiva or Devi are invoked in many different ways. So, how does someone who follows Sanatana Dharma, choose which form to relate to? A form that you will constantly worship to invoke a devotional prayerful attitude in your day-to-day life.
Ishta Devata is the one that you are drawn to, because of your psyche, your cultural, social, and familial background. Kuladevata/Devi is the one whom your family has been worshipping, for generations. Even if your Ishta Devata is separate from your Kula devata, it is good to acknowledge the Kula devata, as a part of your worship, so that the grace of generations of worship can flow through to you. Another way of choosing your Ishta Devata is to go by your horoscope. Your horoscope is a snap of the universe when you are born. Therefore, it gives an idea of the play of fate in your life and what you need to make your life better. For example, if your Jupiter (Guru) is at its peak, then you worship Vishnu or Krishna so that your fortunes and life can be better. If Mars (Mangal) is an issue, then you worship Durga Devi. And so on.
These are the three main ways of choosing which form to worship. Therefore, you can always have an Ishta Devata and acknowledge and worship other forms as time and fate demand. Additionally, if you’re going through a phase in life when you’re faced with a lot of obstacles, worship Ganesha for some time. If you have a problematic time because of Saturn (Shani), worship Saturn directly or invoke Hanuman or Shiva. The beauty of Sanatana Dharma makes it inclusive and practical with a depth of wisdom.