This is my “Book of Positive Aspects” exercise for my own Mother but reading it may be useful for you in feeling appreciation for your own Mom too, be it for Mother’s Day or just to line up with the high vibrations of appreciation and love.
Here’s my personal appreciation exercise:
I appreciate the fact that you looked after me so well throughout my life.
I appreciate how when I was in your tummy you were so careful with what you ate to keep me happy and feeling well as I was growing inside you.
I appreciate that you made the effort to breast feed because you thought it was the best thing for your baby.
I appreciate how you looked after me throughout babyhood; feeding me, loving me, clothing me, waking up for me in the middle of the night if I neeeded you, comforting me, giving me hugs and kisses, caring for me.
I appreciate how you always found something for me to do to keep me interested and occupied.
I appreciate how you encouraged me to start drawing and always made me feel like my creations were beautiful and valuable. I appreciate that you kept them all to this day!
I appreciate how you would sit in our bedroom at bedtime and sing songs like “Teddy Bears’ picnic” and “Way down Yellowgeli” to us to help us get in a sleepy mood.
I appreciate how you would actively keep an eye out to seek out the best play parks for us to play in, and were happy to take us to play often.
I appreciate the effort taken to have taken us to kindergarden and later school, and picked us up again, every week day for years.
I appreciate all the lunches you packed for me for school all those years; taking care and thoughtfulness to make me things you knew I liked.
I appreciate how you drove me over to friends houses and encouraged me to invite friends over to our house.
I appreciate how you’ve always cooked delicious and healthy food for the family.
I appreciate the super-special meals you made the effort to cook on special occasions like festivals and birthdays. The delicious roasts and the amazing cakes and desserts… mmm… 
I appreciate how you’ve always kept a clean and tidy house for us, giving our home a comfortable and pleasant, cared-for feeling.
I appreciate all the care you took to make sure we had clean, well-fitting, nice-looking and ironed clothes.
I appreciate every time you bake cookies, a cake or bread and the whole house fills with delicious baking aromas.
I appreciate how you drove me to piano class every week for years.
I appreciate how you drove me to swimming lessons.
I appreciate how on holidays, you’d take us with you and you’d find things to do that also appealed to us kids, like picking flowers or stopping by to buy a Pink Panther marzipan sculpture.
I appreciate you used to often say “Love it!” as you gave us a kiss.
I appreciate how you always made me feel safe.
I appreciate how you always made me feel loved.
I appreciate how you made me feel like you knew exactly what to do at all times. It was comforting to feel like you had all the answers.
I appreciate how you always make time to listen to my stories.
I appreciate how you always make time to sit down with me when I need to talk something through.
I appreciate when you are eager to help me interpret my dreams.
I appreciate when you give me a hug or a kiss completely out of the blue, as if you you are suddenly overcome with love for me
I appreciate when you look at me with love and compassion in your eyes. 
I appreciate when you give me pep talks.
I appreciate your good intentions when you save newspaper clippings for me that you think will be useful for me.
I appreciate your thoughtfulness when you see something I may like when you’re out shopping and think of me.
I appreciate it when we get along really well together and there’s this feeling of love, comfortableness, ease, flow, interest / stimulation and good energy in the air.
I love you!
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Side note on this appreciation exercise:
I noticed that sometimes when you remember things you appreciate that occured in the past, it can feel a bit like mixed vibrations (eg when I think of being driven to a school that I didn’t like going to, it’s not exactly a fun feeling, even though intellectually I appreciate my mum’s effort to have driven me there). And instead of generating high vibrations it can generate other feelings. I think it may be better for future rampages of appreciation to concentrate on things that feel purely good right now, rather than writing down stuff that you intellectually know you should write “for completeness sake”.