Some people get a little bit scared when it comes to making interior design changes. Of course some people become concerned because things can get costly when you start considering making major changes. That is a real consideration that should be taken into account. But if all you are looking to do is make some simple and inexpensive changes, you should try to not worry too much about it. It is, after all, your home, and there is no "right" way for it to be decorated or designed. The most important thing to consider is how you will feel living in it. If others like the way it looks, that's great, but in the end, you have to be the one who is happy.
Each room that you decide to take on should be seen as an opportunity to express yourself. Updating to a more modern interior design will be more or less involved depending on what you are starting with in the first place. If you are looking at a major project, you may want to look at possibly consulting with a professional interior designer. If that is not something that you are interested in, you may want to at least consider getting yourself some interior design software that may help you to visualize what your finished project will look like.
The kind of space you are starting with is very important. A major goal of interior design that is often overlooked is taking the space you are starting with, and making it work well with a blend of both function and form. Too many people focus solely on how a room will look when a project is complete. This is fine if you are simply trying to set up a showroom, but most people actually will be living in the homes they are designing and they cannot afford to have any non-functional space.
If you are dealing with a small area, like a condominium, you will want to do all that you can to make the most of limited space. Designating certain areas for multiple purposes just makes sense. The area that serves as a dining area may also have to pull double duty for entertaining when guests come to visit. On the other hand, if you are considering loft interior designs, you will want to take into consideration the possibility of smaller pieces of furniture looking lost without some design help.
Whatever your situation, try to make designing the interior of your home fun. If you share the space with another person, be sure to consult them during the designing phase. Get as detailed as possible as you come up with a plan for your dream home. Do things right the first time and you will not find yourself remodeling again in two or three years.