If your tone is sounding brittle/thin when picking single notes, there's a lot of things you can do simply with the adjustments on your guitar or amp.

First, your pickup makes a difference. Depending on your guitar, you can try using the neck pickup to get a more rounded, full tone. You can also roll your tone knob back from the highest treble setting to bleed off some of the highs. Most tone knobs are tapered knobs, so they can be a bit useful after about a quarter turn - just beware of that.

Second, you can do similar adjustments via your amp. Your amp should have either a tone knob or seperate EQ knobs labeled "Bass", "Mid", "Treble". It might have all of these or a combination of them. If it has a "tone" knob, rolling the knob to the left will tilt the eq in favor of bass tones and to the right will tilt the tone in favor of treble tones. If you want to make a "rounder" tone, roll back the mids and push your lows and highs a bit. This should give a wider sounding tone that isn't as "punchy".

If these tips don't get you were you want to go, you can do what some people here have suggested and move into the land of pedals... EQ pedals, compression pedals, boost pedals with EQ control are all tone shaping tools that can get your tone where you want it with a little tweaking.

Obviously without hearing exactly what you're looking for, it can be difficult to suggest things. These are just some basic things you can try with the equipment you already have.