First of all, I suspect new writers don't need my ideas. You have to have SOME notion of what you think would be fun to write, otherwise you wouldn't want to write at all.In that case, I suggest you think long and hard about the elements you think sound fun to write. Make a list. There are no wrong answers here, just what sounds fun. Then pick one that resonates with you. What is it about that idea that sounds cool? What can you picture? What makes that idea attractive to you?
Let's say you wrote down "pirates" and you thought that sounded fun to write about (I picked pirates because it's one of the easiest ideas to latch onto, and also I wrote two books with that as the seed concept).Now, you ask yourself: what attracts you to this idea?
Write down all your initial impressions. Maybe you like the fast-paced swashbuckling swordsmanship from the Pirates of the Caribbean movies, or you want battles on a spray-slick deck, or the vast silhouettes of sea monsters passing under your ship, or the mystery of a buried treasure on an uncharted island, or the adventure of sailing off into an infinite and mystical world.
Maybe it's the mundane, un-romantic side of pirates that interests you. The gritty details that make it seem real, tangible, possible. Pirates would stink like a week-dead dog, they would stab a man to death over a spilled drink or an angry word, they would have rotted and twisted teeth and they couldn't say two words without cursing.
Doesn't matter, but something in that broad idea should fire your imagination. When it does, that's the seed of your story.If nothing fires your imagination, then...what are you writing about? What passion is driving you to write? Why write at all? When the story isn't going the way you want, and you HAVE to get this scene does but it's flowing like a sack of gravel pulling uphill and all you want to do is burn everything you've ever written and start over, why keep going? What makes you WANT to do this?
I also don't think you're bad at coming up with ideas. I don't think anyone is, I just think it's a skill some people don't practice.You can literally take any noun and come up with a story idea. I used the random noun generator from <desiquintans.com> just now and came up with these:"Cake." A down-and-out cake shop owner turns to her skills as a retired jewel thief to compete with her new rival."Dressing." A man tries to cook Thanksgiving dinner for the first time, but finds that he has no idea what "dressing" is and only ten minutes before guests arrive. What will he cook?"Tutu." A police detective finds a break in a long-cold case of a missing ballerina when he finds her bloodstained tutu in the back of his own closet."Wish." ...too easy, pass.That's an example of the first story I thought of for each noun.
Now I apply what I already know about my tastes, and I go for a story I'd actually write:"Cake." A young baker's apprentice finds that she can bring her confections to life as a sweet-but-deadly golem army."Dressing." An architect finds that the ornamentation around an ancient castle's windows hides an eldritch secret."Tutu." A blessed tutu grants increased grace and agility to its wearer, so a young man uses it to fight crime."Wish." For real though, too easy.You can do this too. It's easier for some people than others, but anyone can do it. I believe in you.I think that's the most useful writing exercise you can practice at this point. Come up with ten story prompts that sound interesting to you.
You could just write one of the examples above, I wouldn't mind, but I think you should stretch yourself to come up with an idea based on your own vision. If you really are "bad at coming up with ideas," and I'm not convinced that you are, the way to get better is practice!