Go to the websites of every cruise line that you have even a slight interest in sailing, and sign up for their emails for special deals. If you already know when and where you want to sail, try poking around in cruisetimetables.com. Plug in some places you want to visit using the tab ‘cruises to’, then choose when you want to go. It will tell you who calls there and their itineraries. It is purely informative, not a travel agency.
Once you have narrowed it down to a few, go to the boards here for those cruise lines and ask questions there ( presuming you have some). Go to the websites of the lines for the ships you have listed, and try a dummy booking, going all the way until you have to pay to see what you might pay. Then call your recommended TA, and maybe a few others you have found online ( we can’t recommend any on CC) to see what they can offer you to book with them. EM