For your information, I have been working in Hotel Industry for almost 3 years. I met a lot of tourists in different category in life and I noticed the things that they are looking for an accommodation.
1. Most Touristic Place
While researching for your next destination, better check the locations of tourist destination of that certain city that you are interested in. You do not have to visit all the places in that city, you may rely your destinations based on your preferences. There are website that may help you such as Google, Tripadvisors, travel blogs, etc. You should know the location of those places, if they are in the north or south, east of west. By that you will know the best location for your accommodation and also how you are going to do your itinerary.
It is always the best to get an accommodation near to the places you are planning to visit or the centre of the city. By that, you will not have to spend too much money and time for the transportation. And you will have more time visiting and exploring the city than spending your time inside the bus or a train.
You should know that it is not about if it is an hotel or an apartment, it is all about comfort. Travellers should stop thinking that staying in a hotel is way better than apartments. Dear, there are a lots of apartments that feels like home and they are cheap. And hotels that malfunctions happen even you spend hundreds of bucket for it.
Better to look for the photos of beds that they have. By that, you can distinguish if it is going to be comfortable or not. The photos says it all. You can also check the size of the room. Do not be decisive if the photo is taken by a fish eye lens. And of course, the reviews.
Traveling solo or with friends or family, you should set a range of money you would like to spend for your accommodation.
You should think and analize how much money you are willing to spend for your airfare, accommodation, transportation, foods, allowance and emergency fee.
I always travel with friends. So every time I reserve for an accommodation, I always put in mind that each person should spend 20 to 30 euro per night. If you are 4 in the group, that will be 80 to 120 per night and I am sure you can already find a good accommodation by that price.
Reviews are the most important thing to look for while you are looking for your best accommodation. Before reading the reviews, make sure to check how many guests they already had.
Read all the positive and negative reviews about that accommodation. It will help you a lot on choosing your accommodation.
Make sure you ready the most recent reviews and not those from 2 years ago. The establishment may already been renovated or changed.