Here are some things to consider to keep your eLiquid fresh as long as possible:

• Keep it in an amber glass bottle. This helps to keep light and air out.
• Store it in a cool, dark place. A refrigerator is often fine.
• If it's DIY liquid it will also last longer in the DIY form, so we'd recommend not mixing it with flavorings or cutting it down with PG/VG for storage. Just make batches of flavored as you need them. Our experience is that for a 1-pack-a-day smoker, 30 mL lasts about a month, so making 30 mL of total volume at a time might work well.
• As a DIY eLiquid, there are literally only two ingredients, nicotine and either PG or VG, whichever you ordered. Adding other ingredients can introduce contamination and depending on what you use for flavoring, can introduce ingredients that can spoil. We use natural ingredients wherever possible, which last a long time. However, some of our flavorings do contain artificial ingredients that will impact storage.
• Lastly, for maximum freshness, we do custom manufacture each order from fresh ingredients after the order is placed, so your order was likely manufactured 1 day after you placed the order. The industry consensus seems to be that flavored eLiquid has a shelf life of about 2 years. If you store your eLiquid per the instructions above, it should last at least that long and probably longer.