Watch the Start Solos with the Melody online guitar lesson by Robbie Calvo from Lick Logic
A great way to introduce your solo into a piece of music is by referencing the vocal or instrumental melody. This approach eases the listener into your solo from a place of familiarity, which is a really good thing. An example of this would be to play the song "Ain't No Sunshine". The vocal melody is very distinct and memorable and we've all heard it a million times. Learn the melody or a close version of the melody and start your solo using those notes. Once you've established the pace and feel of your solo, you can either further embellish those melodies or take it to a new and fresh place.
What you've achieved by this approach is a smooth transition of musical sections, taking your listener on a similar musical journey and giving yourself a great place to pivot around for your solo. I do this all the time when I play live and it never fails to be a really nice way to say something melodically without any pressure to be flashy or run out of ideas before you even begin.
1) Play the melody line 4 times, which could constitute a full solo. Then, play an 8 bar solo not using the melody. To come back out of your solo, reference the melody again for 8 bars. It's a really great approach and even gives the band a cue to the end of your solo.
2) Play the melody line and immediately after it play a lick or phrase, almost like a fill between melody phrases. Repeat 4 times and there's your solo!