I use the notes app too! I have an ongoing list of all the products I’ve purchased and marked if they’re reviewed or not yet. When I make a new order, I’ll add each item to the list before it arrives, so I can keep track of what I still need to review (this is the completionist in me coming out, I’m at 20 reviewed of 38 so far 
). I’ll make a new note when I’m ready to start putting down my thoughts about an item (I have several in progress notes open for different items 
)
I’ll usually start with my first impressions before using it, like how it looked and felt. After I use it once or twice solo, I’ll write out literally everything I thought about it. I’ll use it along with different toys to see how the sensations change, I’ll use it during foreplay with my husband (and while we have sex, if possible) and add to my notes, including what he thought about it - how it felt for him (like, if it made me feel tighter or if he could feel the vibrations) and how it made him feel (seeing it on/in me, watching me use it, and using it on me himself). If it’s an item I love, I make sure to include any details that might be a con for someone. Once I feel like I’ve got all my notes down about everything I could possibly think about it, I’ll go back through it and delete redundant or unnecessary parts. Then, I’ll usually read through some of the reviews on the site to see if there was another aspect I forgot to mention, like for example, if someone mentions a storage bag coming with an item, and I forgot to include that in my review, I’ll add my thoughts about the look and quality of it. (I try to get all my thoughts written out first though because I know I’d be influenced by the other reviews 
)
I’ve done a couple low star reviews, and it made me feel bad to submit them 
but I write what I’d have liked to have known before buying the product that I didn’t like. I try to be as detailed as I can rather than just saying I hated it or it wasn’t for me, and I make sure to include anything I did like about the product 
I got some good pointers from the reviewing reviews thread, especial for reviewing lingerie, like to include my size and measurements and which size I ordered. I never would’ve thought to include that, but now I notice it’s helping me when I’m browsing lingerie - it’s really helpful if I see a review and the reviewer has the same body shape as me (and I can skip parts of reviews about the fit if the reviewer is very different size)
Now that I’ve finished writing all this, I’m thinking, I’m still pretty new to reviewing, so I wonder if my input will be useful/relevant 
Hope someone finds it helpful 