Some people are more creative than others, but everyone can be creative to some degree. Usually more than they realise. I find I have days when I play new and interesting sounds and others when I just don't seem to get going. It doesn't seem to follow any pattern.
Start with something you like
A lot of music is created from music! Someone plays their favourite tune which really engages their mind. This engagement will often push them to add bits here and there and before you know it you've got a new song. Starting with an existing song allows an easy path into the music. Creating a new song from scratch will be harder but it's also possible.
Let it flow
Don't try and force creativity. It'll most likely just sound weird. Try and feel your way into it. Practice emptying your mind and just let your fingers do the talking! Quite often something that sounds average to you whilst playing will actually be quite interesting. Create chord changes or runs that seem to have something about them and see what others think. Don't be put off if one person is not impressed, get a few opinions.
Why not throw all the 'rules' out the window. Forget the usual scales and create your own. Create your own licks and chords. Then try adding them together and see what happens. You could even try different tunings. Who says your strings must be tuned to E A D G B E. Do whatever you feel like doing. Treat it as an experiment into the unknown. Who knows what you might discover.
But remember - simple is not bad either
Don't worry if you seem to end up with chords or notes from scales used in many other songs. Just because you're not using chords with crazy names doesn't mean you're not being creative. There are hundreds of songs that sound fresh which use the same chords. Some of the best music written is simple and slow. Don't be put off. It's the unique sound you're after don't worry how you got it - well within reason!
Record and playback
Recording what you play is very interesting. I can guarantee it will sound different to how you heard it whilst playing. I often feel the best bits when listen to a recording are the bits I thought were not that good when playing. If you're in a band that jam, record the whole session and listen back some other time. There will almost certainly be music in there that gets your attention. That music can be recreated and turned into something new. There's really no limits to what can be done.
Hope this helps. Thanks for reading.