Keep routers clear of interference - most routers/modems/gateways are not well shielded against electro-magnetic inferference, and they'll work better when away from any possible source of EMI/RFI. At longer ranges, channel bonding can actually reduce your performance by 70%+ ! Simple throughput testing using both channel widths should be performed for your specific location, or simply turn channel bonding off to accomodate weaker signals. This only works for strong signals and small distances. using 40MHz instead of the default 20MHz channels. Only use channel bonding for strong signals - many newer 802.11n routers support channel bonding, i.e. WMM is a subset of 802.11e that is required for products to be certified for 802.11n. Similarly, the 802.11n spec requires devices to support 802.11e ( QoS enhancements for wireless LAN) in order to use high throughput link rates, i.e. Use WPA2/AES and enable WMM - most 802.11n Wi-Fi certified devices will slow down to 54 Mbps if you use WEP or WPA/TKIP security, since the 802.11n specs state that the higher throughput rates can't be enabled if either of those outdated security methods are being used. Don't mix clients - your brand new simultaneous dual-band 802.11n router will slow down by 50% to 80% to accomodate any legacy 802.11b/g clients (while they're activelly transmitting or receiving). Also, many 802.11n network adapters are rated at a maximum link rate of 150 Mbits/sec. Use 802.11ac or 802.11n clients - note that a newer 802.11ac router will not improve your speed if you only use 802.11g/b clients. For reference, see our bits/bytes conversion calculator.
Also, please note that in data transfers, speed is measured in Megabits per second (Mbps), not Megabytes. Real-life actual downstream speeds considering protocol overhead are in the 30-40% range of theoretical maximum speeds for wireless devices, you can find more information -here.
The theoretical maximum speeds for 802.11 Wi-Fi variants quote ideal conditions, transfers in both directions and shared between all network devices. Have realistic expectations - first, please have realistic expectations for wireless network performance. Below is a list of tips to understanding your wireless network issues and improving wireless speed.