All cruise lines cater to a different clientele so are you going to learn? taking the family away? wanting to eat? This is all part of the experience so if you don't pick the right cruise line you won't have the right experience; to find out which line would be best for you check out our Cruise Line article.
Cruise with someone you like
most cruises will want double occupancy rooms (unless you pay the single supplement) and due to this you are going to be stuck in a tight space with this other person. If they make your trip a nightmare, you won't enjoy yourself!
Check the dress code
Now that you know who you want to travel with and what cruise line you like, what about the dress code? Some ships are very specific (ex. business casual) or have a bunch of formal or themed nights that you need to pack for. Things like this can also make or break a cruise for people
Check the weather
Sure you might have found a crazy good deal but is it too good to be true? Have you checked to make sure you weren't travelling during rainy season? how about hurricane season? Going on a river cruise, what about low tide? Not a fan of the heat but going when humidity is the highest? Poor weather usually means low / off season which in turn will give you the best deal. If you are find to tough it out or take the risk then you'll be fine but if you are not one that can then this can also ruin your cruise.
Comfort
When it comes to comfort, what does that meant you? High staff to passenger ratio so you are waited on by people who know your name? Being able to eat at the drop of a hat? Having access to healthier food options and the spa? Everyone is different and when you do go to book make sure that your "comfort" comes first. This brings me back to not just the budget but also the match preferences as well as picking the stateroom for you.
I've always told my customers that if you have a dream as to what you want your cruise to be and you find out you don't have the budget for it, save. It's far better to get the trip you want then the trip you can afford right now as not only will you have longer to save but you will also not enjoy yourself to the point of what you want.
Don't rush it, savor it!