It never really goes away. It has been 15 years and a roller coaster ride of grief. I try to tell myself that's just the way it is. Obviously I can't do anything about it, but it hurts like it is day 1.
It is always tough for me. I try to do things that I would have done with the person when they were alive. Sometimes, that can yield a bit of joy even in times like that. Around their birthday, holidays, etc is really when I have a hard time. It has gotten slightly more tolerable over the last year, but I still have some days when I struggle to find answers to your question myself.
You don't need any tips, let yourself grieve. Don't suppress it and it will pass. Suppress it and it won't. Anniversary depression is a common thing even in folks who don't suffer from depression. It's really a thing. I've never had it personally, but I've read about it. It will pass. All the best.
Oh, I am so very sorry. I lost my mom and it has been a couple of decades and I still hurt inside because of it. just a sadness. I get it. And this is fairly new for you. So, one thing my sister and I did definitely on the first anniversary (and on each holiday that year) was we did none of our normal traditions. We went out to eat on Thanksgiving. We went out of town on Christmas. And on that first anniversary of her death, we planned a weekend in a city a couple hours away. So we were doing something distracting on that day. I don't know why that worked but it definitely helped us.
And then on the second anniversary and probably most after, I took it as my day. I was extra kind to myself. I went and shopped (which I don't do for myself much) and got a little something for myself. A purse one year, a home décor item, a pair of shoes. Just one thing that I really liked. May sound a little selfish but I do for everyone else and this was my treat in honor of my mom for me. :>) I also always took myself to lunch. I don't do that so much anymore but mostly because I have kids and hardly have the time for that right now.
On that anniversary day, I always have some quiet moments. I have a little conversation in my head with my mom. I feel like I'm talking to her which may sound crazy. But it is very comforting to me.
Now, it's been not much time since your dad passed. And brain cancer is awful to watch. I did some grief counseling after my mom died. It REALLY helped. So, maybe that is something to consider. hugs