I’ve listen to many songs where there’s a lead guitar part that is very slow and not that impressive, but the song sounds amazing, But when I try to play them they just sound like some notes and not that nice melody line, how do I make my solos less lifeless?
What you need to try and do is convey mood and emotion with your music. When you are having a conversation with somebody you don't talk in a robotic, monotonic way. You vary your voice to communicate your meaning better. You need to do the same with your music.
There are (at least) three basic things you can do:
- Vary dynamics. Play some notes louder and other notes quieter, softer.
- Small variations in rhythm. Obviously if you are playing with other musicians you have to go easy on this. You can play some notes fractionally longer than marked and others fractionally shorter.
- Add ornamentation like grace notes or vibrato. These can add complexity and interest.
Exactly what you do and when is up to you. There is no "absolutely right" way to do this. Doing this kind of thing well is what "musicality" is about and doing it really well is difficult, takes experience and talent and is what separates the pros from the merely technically proficient musicians.
Of course before you get to the "musicality" level you have to master the "technically proficient" stuff first. Otherwise it's never going to sound good.
It's not so easy to describe in general. One starts with a good melody. That in itself is worth a couple of books. Then phrasing is important. some notes need to be connected and some separated. It's good to study some melodies by good composers, pop, Latin, classical, etc.
Other techniques (many derived from listening and practice) include adding ornaments (finding which sound nice in the style you're playing in) putting in some connecting tones (like passing or neighbor tones) to give a bit of life to the melody. It's also useful to vary note values; some long notes contrasted some short patterns.
All these take a lot of study, listening, and practice. Try out various techniques; see which ones work; add those to you bag of tricks.
You are asking for advice on something very subjective. Your original question reveals something about your preconceived notions about what is "impressive".
No one can quantify what sounds good for another person. I might say Jeff Beck is one of the greatest guitarists around and his solos are always impressive and full of feeling and someone else here could disagree and say David Gilmore is better. Someone else could say everyone but Yngwie sucks. How can anyone quantify objectively what makes a "good solo"?
I would ask you to clarify one thing about your question.
"But when I try to play them they just sound like some notes and not that nice melody line"
What is it you are trying to play? Your own solo, or the solo you heard? That makes a big difference in terms of the advice I'd give.
If you are trying to play someone else's solo then it might not sound the same because you don't have the techniques down that the player is using. You might also not have the same set up and effects. If your favorite guitarist is using reverb, chorus and a little delay and you're playing the solo clean or with a little distortion it just won't sound the same.
Learning other people's solos is a great way to develop technique. When it comes to playing with feeling I would put phrasing at the top of the list. Passing tones can make a solo sound compressed and drool. I like them but the have to be used wisely. For me, and this my opinion not a scientifically testable fact, large jumps give a solo more "feeling". Some of my favorite Jazz players do use chromatic passing tones and blues licks but they leap up 5ths and octaves and that's what really moves me. I cited Jeff Beck and David Gilmore for a reason. A great number of guitarists love their playing. Beck in particular has phrasing that really affects my mood (positively). Bending adds another dimension to the notes but phasing is all about timing and playing with timing can make a large impact with little effort.
When it comes to playing with feeling it's a not so much what notes you play but HOW YOU PLAY THEM. I'd take a simple three note lick and try to play it several different ways, (1) just pick the notes, (2) use hammer on and pull off (slur) techniques to connect them, (3) bending the lower note up in to the higher notes, (4) glissando (slide), (5) A combination of all the above. The great players bend, trill, and slide all at once (or so it seems). This adds a lot of depth and dimension to a simple idea. Also, repeat yourself. Music is about repetition of patterns and meandering around scales will sound tired real fast. Again, take a simple lick and playing differently each time you play it, same note but different inflection. First time picked, second times slide, third time bend. This kind of thing goes a long way. Listen for these ideas in your favorite guitar solos and learn from imitating.
There's a heck of a lot more to any solo than just the notes played. Obviously they're a great starting point, but that's just what they are!
Are you playing those same notes with the same sound as the guitarist you try to emulate? Playing an open string where he plays a fretted note on a lower string will give a different sound.
Are you playing with the same effects, same amp, same speakers? They will help but are nowhere near enough equipment to copy faithfully.
Are you phrasing the same? Not cutting notes short, sliding instead of bending, plucking instead of hammering-on.
Are you aware of the different attck being used? Some quieter, some louder notes.
Are you using vibrato, especially on longer notes (which are more common in slower pieces), and is that vibrato anything like the original?
Are you aware that your state of mind will have an impact on how you play? And are you capable of putting yourself in the appropriate 'zone'?
Can you vary, even subtly, the phrases being played - so they become slightly different from the original, but still just as beautiful? Phrasing, volume, extra/changed/fewer note, rubato - all these factors make the guitar talk, and delivering a good solo is about that - the delivery of those notes I mentioned at the beginning.
I agree with all the answers I've seen posted so far. But I'd also like to point out that there are Mastering techniques used in the recording process that we never seem to take into account. Mixing, equalization, compression, Phase adjustment, and more can add or detract appeal when we listen to a recorded performance and it just totally amazes us. There are times when a live performance is seriously unable to replicate the music we've grown accustomed to hearing on our home stereos because the acoustics of the room are problematic or the sound engineers don't have the tools and/or skills needed to make it happen. The musicians need to be skilled and have the equipment they need to accomplish the creation of their art, that's a given, but don't forget about the recording techniques and mastering practices when you listen to a final recorded project.