This is a topic that I've seen coming up a lot lately - which is probably a good place to start this post with. If you're having a bit of a spiritual slump, lacking motivation, energy, or whatever else - you're not alone. Many pagans find themselves going through cycles in their spirituality, and I don't think I've ever met a pagan who hasn't found themselves in some sort of spiritual slump at one point, for one reason or another.
People can find themselves in these situations for all sorts of reasons - not having time to practice due to work, or a health issue, a fear of moving into a deeper practice, laziness, and other reasons.
Still, no matter what the cause is, there's really just two things you can do... First, you can recognize that you will have such cycles, and simply accept that as part of your spirituality. I'm sure there are those who think this is probably awful advice, but look, sometimes things are just what they are. If you're the type who goes through these cycles, there's nothing wrong with choosing to work with that, if that's what you want to do.
And doing that doesn't necessarily mean totally ignoring your spirituality for that period of time. You may choose not to do things like daily devotions at an altar, meditation, and so on - but you can still have a spiritual mindset during these times. A nod to the sun or moon while out on a walk, spending a bit of time thinking about the seasonal cycles during your commute, and so on.
Alternatively, one could find a way to just power through these times. Establishing some sort of daily practice can be helpful in this, and truly, it can be helpful in preventing slumps in the first place. If time is a problem, it's good to try and tie your daily practice in with something you'd be doing anyway - a prayer over a meal, a small devotional while dinner cooks, a purification while showering. Any somewhat consistent time can work well though, like after getting up, before going to bed, or whatever works for you.
Having some sort of visual reminders can also help you remember/motivate you to practice. An altar is, of course, a great reminder - but anything can serve as such a reminder if you put the association to it. Jewelry is also great for this... it doesn't have to be something obvious like a pentacle, again, anything can really serve as a reminder if you consider it to be one.
When you're in a slump (and even when you're not), it's important to think about what you want to do, and why you want to do it. Is it something you truly want, or is it simply something others have made you feel you need to do? If it is something you really want, if there are goals you have, it might take a bit of work to get yourself there... but, chances are it'll be worth it.