Some people swear by a 1:1:1 ratio, but I’ve found that never works for me. My starter always ends up too runny and not very strong. I was doing a 1:1:.75 ratio at one point, but I’ve found my starter sometimes becomes sluggish and doesn’t peak as quickly because it’s not getting enough food. So I’ve started to do a 1:2:1.5 ratio (I honestly don’t know if that’s a real ratio haha, but it works for me). For example, I would do ½ cup starter to 1 cup flour and ⅔ cup water. If you don’t want to keep that much starter on hand, you can lower it to ¼ cup starter to ½ cup flour and ⅓ cup water. This will ensure your starter is getting enough food and is always strong for bread or other yeast recipes. You can also use it to make a new starter, heaven forbid your current one accidentally dies, gets mold, or gets baked in the oven  (I get a lot of those messages).