A great place to start with interior design and decorating is to think about each room and what you want it to say. If you're after a calming, soothing haven to return to after a busy day at work then you'll need colours that reflect that - neutral, classic tones work well, as do pastels. Perhaps you want your home to be the very picture of hospitality, so you'll let that guide you to choose warmer tones. Maybe you want your house to reflect your personality, so will be choosing bold, striking colours and bright feature pieces to make sure it really pops.
Don't even think about picking up a paintbrush until you've made your first moodboard. That might feel like the realm of a professional creative, but it doesn't have to be. Even if you end up hiring an interior designer, having your initial ideas mapped out in this sort of format will only help them to better understand your vision. Depending on your preference you can create a board by cutting out magazines, pasting photos, fabrics and colour swatches on to your board - or you can use a tool like Pinterest to pull together visuals you love from around the web into one place. Either way, you'll find as you go through this creative process that one idea sparks another and you start to build a clearer picture in your mind as to what you want. Take your board into the room you're decorating and see how the colours work in the light and with any existing fixtures or furnishings that you'll be keeping.
A tonal scheme is the simplest to pull off well - start by nominating your colour of choice that will be the consistent element through your home. Then you select different tones and shades for each different area. This means a feeling of consistency and harmony will run throughout your home, but each room will still retain an element of individuality. You can choose the tone to suit the room - for example, if green was your selected colour you might choose relaxing, earthy tones for the bathroom and bright lime features for an energetic area such as a playroom. You can use tools such as a colour wheel to see what colours work well together and will complement each other.
This is the final stage at which you might choose to consult an expert. If you're not a dab hand with a paintbrush then consider contracting a handyman carefully before you push on - don't ruin your hard work with a poor finish. If you're confident however, then start by painting large sections of the wall with paint from sample pots. Ensure you paint different areas of the room so that you can see how your colour looks under different light. Once you're happy then get decorating!