about uploading wedding invitation

hi i have designed a set of wedding invitation card along with rsvp card, thank you card, menu, and tag but i am really confused as if i how i am suppose to upload them.
also how i am suppose to make a thumbnail of it bcz every time my thumbnails are blurry even though i follow the size and guideline thats given on envato
i am new to envato and have had several rejections before. it is an illustration file if some one can guide me it would be really great thank you in advance