First, don’t get burned out – and know that there will be times when your creativity ebbs. It happens. Don’t beat yourself up. It will come back. Take a break if you need to.
Secondly, try to figure out if you are, what is termed in psychological parlance, as “early starter” or “pressure-prompted” which mean exactly how they sound. I’m an early starter. I’m more creative when I do things ahead of time with less pressure. I have several family members who are extraordinarily creative only if doing things at the last possible moment, so everyone is different. Work to your strengths when you can.
Thirdly, practice. Both technique and sourcing. What does that mean? Keep your design, drawing, etc. skills sharp. Tools like Inktoberare great for this! Use them even when you don’t have a pending project.
Also, take time to figure out what feeds you – in my case music and being outside are big ones – and use them when you need to.