Throughout my years of learning and playing music, I've developed a bit of a philosophy on the best way to practice. I've found some things that work for me and they'll definitely work for anyone who applies them too.
1. Spend Half of Your Practice Time on Stuff You Don't Already Know.
Practicing songs that you can already play through without a problem is fun and encouraging but it isn't useful for making you any better at the instrument. Focusing half of your practice time on something new and challenging will help you push yourself to the next level. It will help you expand your comfort zone and grow as a musician if you keep challenging yourself with new songs that are just outside of your skill level.
2. Record Yourself Playing and Listen to It.
Do this by any means necessary, even if it's just a video or audio recording from a cell phone. You'll notice things about your playing that you didn't pick up on before. You'll discover new holes in your playing and it will help you determine what you should be working on.
3. Learn Songs That Have Both: Lots of Different Chords and Chords That You're Not Good at.
Pick a song that you really like with a lot of chords (like "Hotel California" maybe?) and stick to it until you have it down. This will help you master new chords and allow you to play even more songs. A more recent example of a song with a ton of different chords in "When I Was Your Man" by Bruno Mars. That's a good one if you're looking for some challenging vocals too.
4. Practice With a Metronome/Recording.
Sometimes (not always) you should break out the metronome and play along with it. This will help you to follow a consistent, external beat. It will also help prep you for playing with a drummer. Another way to go about this is practicing with a backing track or a recording. Sing on top of the track, practice soloing, etc. This will get you closer to being able to play with other musicians if you haven't already.
5. It's Better to Practice for 5 Minutes Everyday Than an Hour Once a Week.
When you practice your instrument (or do anything), neurons form patterns in your brain. Eventually the patterns get deeper the more they fire through, this is what determines how good you are at whatever you're doing (playing music in our case). This will happen every time you practice. When you fall asleep, the neurons will refire rapidly through every pattern for everything you did that day. If you only practice once a week, even if it's for an hour or two, this refiring will only happen once whereas it would happen every night if you practiced daily. It's better to practice everyday, even if it's for less time.
Try applying these tips to your practice routine and get more out of your practice time!