I am playing an Archfey Warlock with the "Pact of the Chain" Pact Boon. For thematic reasons, I have chosen for my familiar to take the form of a sprite with the "fey" creature type.
The restriction I place on this question is that the above facts must remain true, these are fixed aspects that I do not want to change; hence any answer that states that the familiar should take another form, like an imp, are not valid answers to this question, regardless of how much more optimal that might be. In other words, this is not "how to optimise a Pact of the Chain warlock", but "how to optimise the use of the sprite as a Pact of the Chain warlock’s familiar".
Further restrictions are that I do not plan on multiclassing, so answers that require multiclassing are also not valid answers, and that I am limiting the range of levels in play to between 3 and 7, so answers that require me to be a higher level warlock are also not valid (although if an answer includes a "here’s what you can do at high levels too" section as an added extra, I won’t complain).
Given these restrictions, I want to get the best use out of my sprite familiar. Because of it’s tiny HP pool, so far I’ve just had it remain invisible and hide out of sight so that it doesn’t get shot and killed, since I’m still currently only level 3 and don’t really want to waste the resources resummoning it (later in the game, I assume this won’t be as much of a problem, but let’s assume that the familiar’s survivability is a concern of mine nonetheless, but not actually a hard restriction).
What are the best tactics to employ to make the sprite familiar as useful in combat as possible during late tier 1/early tier 2 play? I’m happy for people to suggest spells and invocations that the warlock themselves should pick in order to support the tactics that would enhance the sprite’s usefulness, but I don’t want this to turn into a question about optimising the warlock themselves; the focus should be on the sprite (in other words, assume the warlock is already optimised well enough for the purposes of this question).
Related Q&A: What can a familiar actually do? (except this question is about familiars generally, and the answers do not take into consideration the traits specific–if not unique–to a sprite, such as invisibility or potentially being able to poison an enemy or make it fall unconscious with the sprite’s shortbow attack)
Related Meta Q&A: Would this question about when it's better for a Pact of the Chain warlock to have their familiar attack be an on-topic bounded list question? (although no-one seemed to have an opinion either way, so I’ve gone ahead and asked it anyway; however, this meta Q&A can still be used as a platform to discuss the on-topic-ness of the question, should that become necessary)