So the question is are you able to do the job right yourself or do you need to get a contractor in. Well in my experience 90% of the time you are able to do the job yourself. It isn't difficult at all. Firstly you need to do some research, with Google available at your finger tips you can do almost anything yourself. Just open up a search page and punch in what you want to accomplish into the search engine and you will instantly have ten websites that will give you step by step directions on what needs to be done.
You also have to gauge how big your project is going to be. Don't start something and give up halfway through it. Create a project plan and stick to it. For example if you have a wall in your house that has become damp, due to a badly sealed shower or sink, you have to plan and use common sense as to what needs to be repaired first. The obvious answer is, repair the seals in the shower or sink first before you tackle the wall. By searching on the web on how to do this you will know that you have to remove the old damaged silicone seal first by applying silicone stripper and then renewing it with a new layer of silicone.
Once that is sorted you then need to tackle the wall. If the plaster is damaged you may need to re-plaster and this can be a bit tricky to by yourself. By doing a quick internet search you now know what materials you will need. Purchase the materials and then outsource just the plastering to a skilled labourer. Get the plastering out of the way by a the cost of a days labour charge and do the rest yourself. Thus saving you mega bucks.
This was just an example of what can be done with a little research. By doing it yourself you will also upskill yourself and you will become more proficient in DIY. Another trick that I have learnt was to get contractors in to quote you on the job, but be there when they are assessing and ask them what they are going to do and how. Quotes don't cost you anything but you get a good idea of what materials you need to buy and how to do the job.
So remember create a project plan, cost your materials and do your research!