Only 9 lands! Once you add in another 26 or so, you'll need to cut over 80 cards. That's enough for a second whole deck.
Start by cutting the expensive cards that you don't already own. Nobody knows which those are except you.
Then look for cards where you have way too much duplication. For instance, how many "no maximum hand size" effects do you really need? If you use
Reliquary Tower you have that effect on a land.
When you have almost 100 extra cards, either you have too much duplication of effects, or your deck isn't focused enough. (Typically a little bit of both.) So you also want to narrow the focus a bit. Do you want to primarily poison your opponents? Or are you trying to clear the board via -1/-1's so that you can swing in clear with your creatures? Or are you trying to accomplish something else? When you have this many extras, pick just the cards that help achieve your primary objective. Chuck the rest.
Typically you want about 35 lands, 6-10 non-land mana sources/ramp and 4-10 removal card, and a few protection spells (like
Lightning Greaves). This accounts for about 50 cards in your deck. That means only 50 cards that are accomplishing your goal. Some decks want even more ramp, or more removal, or more protection, and have even fewer cards that are "on task".
Happy Brewing!