Approaching lead guitar
There is more than one approach to soloing over chords (or 'changes' as the Jazzers call it). In fact, the approach taken ought to be a combination of more than one approach: a combination of using one's ear and imagination, applying pre-rehearsed licks in all the right places; and also knowing how to manipulate scale and arpeggio patterns in a musically and stylistically convincing way.To give but three examples.
Right here, I want to talk about the scale and arpeggio patterns approach. let's be clear, just going up and down scale and arpeggio patterns is not sufficient. Whilst they provide the notes, you must learn what to do with the patterns in sympathy with stylistic considerations. It's rather like learning lots of foreign words yet not knowing what to do with them. Learning about style has to be an important consideration.
Right now, we will assume that the chord progression to be soloed over is stricly diatonic; that is, in one key with no deviations. It would help if we know the chords that make up the progression from the outset; although anyone with trained ears and experience can quickly recognise what chords make up a progression. From this starting point, it is important to know how each note in the scale/key relates to any given chord in the progression. In particular, you have to be able to distinguish between chord tones and non-chord tones (what are called passing notes). It really helps if you can go beyond just patterns to knowing what notes make up both the chords and the scale/arpeggio patterns; otherwise one is a slave to patterns and ear alone. Not the best situation to be in. And it really helps to have a theoretical framework within which to work.
The quaver should be taken to be the most essential note type. From that, you should learn to play around the scale/arpeggio patterns. I think the methodical approach is to take each singular diatonic chord that the key provides, and learn to use the patterns around that chord before moving on to the next chord. Then repeat the process for a two chord progression; then four. Aim to work within four bars at a time, because it is the typical length of a phrase; and we should be thinking in terms of phrases! Wind players do it naturally.
As a general rule, aim to play chord tones on the beat whilst non-chord tones are played off the beat. And be able to work out what the relationship is between any note played and the chord played over. So for example, whether a given note is the 3rd of the chord or the 5th or in fact a 6th or b7th etc...It isn't enough just to play patterns mindlessly, or to simply rely on the ear or set patterns. One must be thinking whilst one is playing. At first this thinking process is somewhat slow but it does get quicker with encouragement.