I’m going to jump in here and contradict you with the advice Justin gives here.
If you are not yet able to make use of one scale pattern in a single position on the neck, the worst thing you can do is to learn more scale shapes. You need to get develop techniques and musical know-how to use one basic tool before trying to work with others.
Do you know the key of those songs to therefore play the major scale in the same key? Do you know that they are all in major keys and do not change key?
The minor pentatonic is a more user-friendly and accessible route into playing lead improvisation by learning licks and more. Check out this tip topic to explore that path: First Steps in Blues Improvisation using Minor Pentatonic Scale Pattern 1
Try this …
Play the mp3 backing tracks of each of the chords G, Am, Bm, C, D and Em. and play some short, improvised lines over the top. Listen for the quality of each note over the chord, and especially listen to the first and last notes. Do they sound good / not so good? Remember – a good note is just one place above or below a ‘bad’ note.
Play and focus on just one string at a time as you explore the creative possibilities open to you.
1st string – frets 2, 3 & 5
Pause here and explore what you can do with this string only over each of the drone chords in turn.
2nd string – frets 3 & 5
Pause here and explore what you can do with this pair of string only.
1st and 2nd string.
Explore what you can do with this pair of strings and the five scale notes they contain over each of the drone chords in turn.
Continue.
3rd string – frets 2, 4 & 5
Pause here and explore what you can do with this string only.
1st, 2nd and 3rd strings.
Explore what you can do with these three strings over each of the drone chords.
4th string – frets 2, 4 & 5
Pause here and explore what you can do with this string only.
1st to 4th string.
Take a lot of time to explore what you can do with these four strings over each of the drone chords.
For now, concentrate on just these four strings - it is more than enough and gives you over one octave of the scale.
If you are still finding it hard to make meaningful note choices, phrases and musical motifs then try this for inspiration.
Start with a short vocal phrase.
Say the words rhythmically (long & short vowel sounds and syllables will mean different phrases can be said with different rhythmic lengths and feel).
Turn that rhythm into an improvised melody by using it to guide the timing of your picking as you play notes from the scale.
Examples:
1] Look at the sunrise – wow
2] Gimme a hug, I love you
Anything you want as a short statement. Use repetition to make the statement several times, maybe using different notes, altering the emphasis on certain syllables by making the note shorter or longer.
Longer example:
Hello, it’s great to see you
He-lloooo, it’s great to see you
Hello, it’s grrr-eeeat to see y-oouu
Once you are becoming more and more adept at putting together short, musical phrases over a single drone chord, extend yourself to playing over a backing track with chord changes. You will need to be listening and aware of the way that certain notes sound great over certain chords but ‘less good’ over other chords.
I hope that helps.
Cheers 
| Richard | JustinGuitar Approved Teacher, Official Guide & Moderator