Use WPA2 assuming all your devices (laptops/phones/etc.) and your WiFi access point support it – best security.
If you have poor WiFi coverage in your home use a second WiFi access point located in the area of low signal, give it the same SSID and WPA2 passcode as your main WiFi access point and you devices will “roam” between the two. Use a different channel on your secondary WiFi access point, referring to points 1 and 5.
If you don’t want to run network cables around your house then use a mains networking device instead, I’ve got a D-Link Powerline 500M with an old NetGear WiFi/router on the end of it, my main WiFi comes from my Virgin Superhub.
Use WiFi analyser software to see which channels are being used by other people near you, and make sure you’re using channels that are as far away from them as possible. I use this on my Android phone, but there is similar software available for other platforms including Windows. Or you can get a proper radio spectrum analyzer.