Chandana P. you can try Gamma AI - for something like LinkedIn Carousel images. Have not tried image generator there.
But their basic layouts they offer are very easy to use, and fairly polished.
In terms of prompts you just have to keep testing. When you get a result you like, ask ChatGPT to act as a prompt engineer expert and generate the prompt that would allow you to replicate the result you got.
OpenAI’s new image model GPT-image-1 is pretty amazing. I use it for my linkedin posts and it even gets the text correct. I’ve used it to build workflows that create product images also..Nano banana is great also
Adobe Firefly can generate images from prompts, even in the free version, though with some limits. Alex’s examples also look wonderful, if that’s the kind of output you’re looking for.