I've seen a lot of newer designers hitting this issue with their designs. It's something that can easily be rectified as well! Have a look at these tips to get using a colour palette:
Limit your colours
Don't go wild with the number of colours you are using. By limiting a palette of colours to around 5, you are honing in your colours to that limited palette. By restricting you'll bring some structure to your colour naturally.
Don't use jarring colours
This is a tricky one, but ensure that nothing is harsh to the eye, it's up to you to look at your colours for this. If you can ensure that your colours compliment each other, then you're creating a colour palette.
If you have branding use your colour palette
This tip is for anyone that has had a designer come up with branding for your company. If you have had branding, it's likely that you already have a colour palette, that gives you colours that you should be using in your designs.
Look at curated colour palettes
If you don't feel confident in creating your colour palette from scratch, there are lots of curated colour websites out there. With curated colour palettes you can use the colour palette as it is, or you could take it as a starting point and change it.
These are some great resources to get you started:
Test it with people
Like every tip, I recommend showing your colour palette to people, get it out there and get peoples opinions. The more people you can get feedback from the better. A good thing to test for is what people's initial feelings are to a colour palette. Try and find out more on:
Do they like the colours
What emotions come to mind when they see the colours
What would companies they associate these colours with
Do they think it would reflect your design well
I think by finding out some of these things above, you will find out what the consensus is around your colour palette.