"What kind of pellets are you using" has already been asked, tho not answered. How about: "are you using alloy/hobby pellets?" Lightweight pellets deliver much higher velocity, and usually much "suckier" groups than lead. If you are using lightweights, try lead. The Ruger line all seem to deliver "magnum power" on paper, so I would suggest shooting something in the 8 to 11 grain weight (assuming your rifle is .177), and 16 to 18 grain if it's a .22. Lighter weight pellets that travel in the high 900 to low 1000 fops tend to destabilize as they lose velocity, and "corkscrew" or tumble. Also, the shape of the pellet can contribute to accuracy issues (though not usually at close ranges like 25 yards). If you're using wad cutters, try domes or pointed pellets.
Artillary hold: figure out where the center of balance is for your rifle, and place your support hand under it. Shoot a lot. If your groups don't improve, move your hand forward or back a bit, try again. It takes a lot of practice and experimentation to get it right. When I first started shooting sprinters, my groups at 25 were atrocious! After I don't know how many shots (a lot!) I got my groups to shrink up considerably by experimenting with changing position of my forearm hold, but they still weren't great. Once I bought a Chrony, I saw that my "1200 FPS" gun was actually only hitting about 700 FPS. I rebuilt it with a new seal, and suddenly it was shooting in the 900s, and putting pellets on top of each other. You may consider doing that as well.