Try the songs in other comfortable keys (groups of chords). Sing along and see which ones sound the best. Work a lot on those until you get one or two working well.
Use different rhythms. Just fool around with them. There are thousands of varieties of rhythms so be inventive. Give a song a reggae feel, a rock feel, a blues feel. Try playing so that dancers could do the samba or the merenge.
Then work on playing all four keys and any others that fit your voice.
Make sure your fretting is done right—that the strings ring out and aren’t muted because you aren’t holding them down correctly or have an errant finger touching a string that should be open. Don’t press too hard on the strings. That will lead to repetitive stress syndrome. Press just hard enough to sound good.
Check your posture and correct things so you feel comfortable.
Watch your fretting fingers to make sure you aren’t pulling them too far off the neck when changing chords. You only need to raise them enough for the strings to sound good or to get to the next chord. Don’t be extravagant with those movements.
See if you can figure out a closed chord pattern for the I-IV-V chords. A closed chord pattern has no open strings so it works wherever on the neck. Try to find a pattern just on the first 3 strings. This means you can only strum those strings so now you’ve got to get the right hand hitting more accurately.
And don’t practice all the time. Sometimes, just play the song as loud as you can and don’t worry about anything else.