Please read Durga Sahsranama for 21 days in the mornings or evenings. Its a good starting point.
Please be a vegetarian on the day you read sahsranama and offer whatever little flowers you can to the idol or picture.
Even if you don't have a Durga Devi image, its ok.
Whatever Goddess image you have, offer the flowers in front of that image. Almighty is just One.
Also don't forget to read Durga Aparadha stotram after reading Durga Sahsranama.
And whatever you read, please don't doubt the mantras. There will be mistakes but offer your prayer with full faith.
Durga Devi will show you the rest. You will get your guru when time comes.
And please assess yourself before starting as to whether this is for you or not. You shouldn't get bored after the initial rush of spirituality which happens to many.
Most of the people drop prayers midway.
Hope I helped you.
Take care.