April is your best opportunity this year to see Mercury (or, at least, it is if you, like me, are an evening, rather than morning, person!) Mercury is never very far from the Sun, but on April 18 it reaches its maximum at this apparition of 20 degrees east of it. This means that Mercury will be roughly where the sun will be in the sky in May -i.e further north, and therefore further above the horizon after sunset , and hence easier to spot. The best time to look is about 1/2 hour after sunset, and it is worth trying on any day in the 2nd half of April . You will need a good view of the horizon a bit north of west. I usually scan the area with binoculars first to pick it up, but on a decent evening it will become easy to see with the naked eye. There is a trade off as dusk descends between the benefits of increasing darkness against Mercury sinking towards the horizon. If you have a telescope you should be able to see a tiny crescent but it will be very distorted in colour and wobbly that close to the horizon. For this reason those who want to observe Mercury seriously generally do so in daytime when it (and therefore the sun) are both high in the sky. However, finding it is then with a telescope is a much more difficult, and potentially hazardous business, and should not be attempted unless you know what you are doing.
The other main attraction this month is the wealth of galaxies to be seen in Virgo and Coma Berenices. For this you will need as dark a sky as you can get to, and a moonless night (so the first half of the month), and the largest telescope you can get hold of. The map below gives a good starting point for a tour – 6 Coma Berenices, marked with a red arrow – which is fairy easy to find as in effect marking the end of a tail on the distinctive shape of Leo. The advice is to study the map in the warmth and light at home before you go out, and then see what you can find and identify. Then repeat on future nights, and you will get to know this part of the sky well!